Matched impedance controlled avalanche driver

ABSTRACT

Controlled avalanche driver circuits and apparatuses for gas lasers. One embodiment typically delivers short, rapid, high voltage ionizing pulses in combination with an electric field whose magnitude is too low to sustain a normal glow discharge. The plasma is typically impedance matched with the pulse-forming network. Pre-ionization pulses may be generated. The circuits enable very high power, stable lasers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application of U.S. patentapplication Ser. No. 10/220,541, filed Aug. 30, 2002, entitled “Compact,Flexible, Rapid-Pulsed, Molecular Gas Laser”, issued Aug. 3, 2004, asU.S. Pat. No. 6,771,684, which was a national entry application ofPatent Cooperation Treaty Application PCT/US01/06812, filed Mar. 1,2001, which claimed the benefit of the filing of U.S. Provisional PatentApplication Ser. No. 60/186,430, filed on Mar. 2, 2000, and thespecifications thereof are incorporated herein by reference.

This application is also a continuation-in-part application of U.S.patent application Ser. No. 10/086,030, filed Feb. 27, 2002, entitled“Electric Oxygen Iodine Laser”, which was a continuation-in-partapplication of Patent Cooperation Treaty Application PCT/US00/23642,filed Aug. 28, 2000, which claimed the benefit of the filing of U.S.Provisional Patent Application Ser. No. 60/151,260, filed on Aug. 27,1999. U.S. patent application Ser. No. 10/086,030 also claimed thebenefit of the filing of Provisional Patent Application Ser. No.60/278,329, filed on Mar. 22, 2001. The specifications of theapplications cited in this paragraph are also incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention (Technical Field)

The present invention relates to molecular gas lasers and pulse circuitsand excited atomic state and plasma generators related thereto.

2. Background Art

Note that the following discussion refers to a number of publications byauthor(s) and year of publication, and that due to recent publicationdates certain publications should not be considered as prior artvis-a-vis the present invention. Discussion of such publications hereinis given for more complete background and is not to be construed as anadmission that such publications are prior art for patentabilitydetermination purposes.

SUMMARY OF THE INVENTION (DISCLOSURE OF THE INVENTION)

The present invention is of a gas laser comprising at least onereciprocating assembly, each reciprocating assembly comprising a driverhousing, at least one flow reciprocator, and a driver diaphragm.

The present invention is additionally of a method of producing a laserbeam using a gas laser, the method comprising the steps of providing tothe gas laser a reciprocating assembly comprising a driver housing andemploying within the reciprocating assembly a driver diaphragm and atleast one flow reciprocator.

The present invention is also of a circuit for exciting a gas comprisinga matched impedance controlled avalanche driver.

The present invention employs a pulse circuit for generating an outputpulse, comprising for example a power supply; at least one Blumlein linewherein each line comprises a front end and an output end; a switch forgrounding each front end of the at least one Blumlein linesimultaneously; and a snubber for truncating the output pulse from theat least one Blumlein line. As described herein, this pulser circuit isuseful for a variety of applications. In an embodiment of this pulsercircuit, the circuit further comprises at least two Blumlein linescomprising electrically connected and simultaneously groundable frontends and serially connected output ends. In another embodiment of thispulser circuit, the circuit comprises discharge electrodes fordischarging the output pulse to a gas wherein each of the dischargeelectrodes optionally bound a tube configuration comprising a surfacefor heat exchange.

The present invention also comprises an inventive generator forgenerating an excited atomic state of a molecule. According to oneembodiment, this particular generator comprises a power supply; a pulsecircuit; and an excited atomic state generating region wherein the pulsecircuit discharges a pulse to a gas in the region and thereby generatesan excited atomic state of at least one molecule in the gas and whereinthe gas optionally comprises at least one inert gas. In a particularembodiment, the excited atomic state generating region optionallycomprises electrodes, a loop, or a cavity wherein the cavity optionallycomprises a resonant cavity or a capacitively coupled cavity(particularly useful for RF and microwave energy deposition). In anotherembodiment, the excited atomic state generating region optionallycomprises a loop and at least two electrodes. In yet another embodiment,the excited atomic state generator optionally comprises an excitedatomic state generating region comprising a loop and at least onetransformer core comprising at least one winding wherein the excitedatomic state generating region loop forms a second winding of the atleast one transformer core. In many of the embodiments of the presentinvention, particularly the generator and laser embodiments, removal ofheat from the system is useful. For example, one embodiment of thegenerator comprises an excited atomic state generating region thatfurther comprises a component of a heat exchanger.

The present invention also comprises a laser. In one embodiment, thelaser comprises a power supply; a pulse circuit; an excited atomic stategenerating region wherein the pulse circuit discharges a pulse to a gasin the region and thereby generates an excited atomic state of at leastone molecule in the gas and wherein the gas optionally comprises atleast one inert gas; and a resonant cavity for generating a laser beam.In a particular embodiment, the laser optionally comprises a heatexchanger for controlling the temperature of said excited atomic stategenerating region; and optionally comprising supersonic expansionnozzles for introducing the gas into the excited atomic state generatingregion.

The present invention also comprises several inventive methods. Forexample, the present invention comprises a method of generating aplasma. In one embodiment this method comprises the steps of: a)providing a gas; b) applying a pulse to the gas to over-volt the gas toan E/N value above ionization breakdown thereby forming a plasma; c)applying additional pulses, above ionization breakdown of the gas, tosustain quasi-continuous ionization of the plasma; and d) causing acurrent flow to the plasma by applying an electric field comprising anE/N value less than the glow potential of the plasma. In a particularembodiment of this method the gas comprises O₂ and the method generatesan excited atomic state of O₂ and optionally wherein the excited atomicstate comprises O₂ ¹Δ.

The present invention also comprises a method for producing a laserbeam. In one embodiment, this laser method comprises the steps of: a)providing a gas; b) applying a pulse to the gas to over-volt the gas toan electric field normalized to plasma density value above ionizationbreakdown thereby forming a plasma; c) applying additional pulses, aboveionization breakdown of the gas, to sustain quasi-continuous ionizationof the plasma; d) causing a current flow to the plasma by applying anelectric field comprising an electric field normalized to plasma densityvalue less than the glow potential of the plasma; e) contacting theplasma with a molecule of the gas to generate an excited atomic state ofthat molecule; f) contacting the excited molecule with iodine to excitethe iodine; and g) lasing the excited iodine.

The present invention also includes a laser comprising a gas, a beamproduced by the gas and a throat wherein the gas and beam pass throughthe throat. In one embodiment, the throat comprises a converging regionand a diverging region to achieve supersonic flow of gas passingtherethrough. This particular embodiment is optionally useful when alasing molecule is capable of repetitive cycling over the length of acavity. While iodine is suitable as a lasing molecule, this embodimentis not limited specifically to iodine.

A primary object of the present invention is to enable an electricoxygen iodine laser.

A primary advantage of the present invention is an efficient laser.

Another primary object of the present invention is to provide a compact,flexible, rapid-pulsed, molecular gas laser.

Another primary object of the present invention is to provide acontrolled avalanche driver circuit.

Other objects, advantages and novel features, and further scope ofapplicability of the present invention will be set forth in part in thedetailed description to follow, taken in conjunction with theaccompanying drawings, and in part will become apparent to those skilledin the art upon examination of the following, or may be learned bypractice of the invention. The objects and advantages of the inventionmay be realized and attained by means of the instrumentalities andcombinations particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and form a partof the specification, illustrate several embodiments of the presentinvention and, together with the description, serve to explain theprinciples of the invention. The drawings are only for the purpose ofillustrating a preferred embodiment of the invention and are not to beconstrued as limiting the invention. In the drawings:

FIG. 1 is a schematic side view of a laser embodiment of the presentinvention;

FIG. 2 is a schematic side view of the laser embodiment shown in FIG. 1;

FIG. 3 is a schematic top view of the laser embodiment shown in FIGS. 1and 2;

FIG. 4 is a schematic of loudspeaker driver and driver circuit accordingto an embodiment of the present invention;

FIG. 5 is a plot of Rayleigh heating curves;

FIG. 6A is a plot of plasma voltage and current waveforms generated byan ideal matched impedance controlled avalanche driver according to anembodiment of the present invention, voltage and current valuescorrespond to parameters for a 0.5 ATM, 10 liter volume laser with apump current plateau of 12.5 kA and τ of between approximately 100 andapproximately 400 nanoseconds;

FIG. 6B is a plot of plasma voltage and current waveforms generated byan actual matched impedance controlled avalanche driver according to anembodiment of the present invention, plasma load is approximately 0.5ATM with a 0.5 liter volume discharge and the upper trace is plottedwith 10 kV per division and the lower trace is plotted with 400 A perdivision, both having a time base of 2 microseconds per division;

FIG. 6C is a plot of plasma voltage and current waveforms generated byan actual matched impedance controlled avalanche driver according to anembodiment of the present invention, plasma load is approximately 0.5ATM with a 3 liter plasma volume and the vertical scale is 1200 A perdivision having a time base of 0.5 microseconds per division;

FIG. 7A is a schematic of a hybrid pulse former circuit according to anembodiment of the present invention;

FIG. 7B is a schematic of a hybrid pulse former circuit according toanother embodiment of the present invention;

FIG. 8 is a graph of a variety of reactions versus E/N in Townsend;

FIG. 9 is a perspective view of a loop configuration of a generatorembodiment of the present invention;

FIG. 10 is a perspective view of a loop and electrode configuration of agenerator embodiment of the present invention;

FIG. 11 is a cross-sectional view of a loop and core configuration of agenerator embodiment of the present invention;

FIG. 12 is a diagrammatic view of a generator embodiment of the presentinvention;

FIG. 13 a is a diagrammatic view of a tube bank of a generatorembodiment of the present invention;

FIG. 13 b is a diagrammatic view of a housing of an embodiment forhousing a tube bank, such as that shown in FIG. 13 a;

FIG. 14 is a graph of excited oxygen species shown as density versusdistance for a particular embodiment of the present invention;

FIG. 15 a is a diagrammatic side view of a laser of an embodiment of thepresent invention;

FIG. 15 b is a diagrammatic view of an injector block of an embodimentof the present invention;

FIG. 15 c is a diagrammatic top view of the laser shown in FIG. 15 a;

FIG. 16 is a diagrammatic view of a close-cycle laser according to anembodiment of the present invention;

FIG. 17 is a diagrammatic view of a pulser circuit and generatoraccording to an embodiment of the present invention;

FIG. 18 is a diagrammatic view of a controlled avalanche circuitmechanical assembly according to an embodiment of the present invention;

FIG. 19 is a diagrammatic view of a circuit for floating a DC potentialon top of a DC jump potential and a pulsed high voltage avalancheionization potential according to an embodiment of the presentinvention;

FIG. 20 is a diagrammatic view of an embodiment for producing a beamsubstantially parallel to the direction of gas flow; and

FIG. 21 is a diagrammatic view of a beam of the embodiment shown in FIG.20.

DESCRIPTION OF THE PREFERRED EMBODIMENTS BEST MODES FOR CARRYING OUT THEINVENTION

The present invention provides for lasers with very high peak powerpulses of variable duration, from approximately 0.1 μs to greater thanapproximately 10 μs, that are continuously pulsable at repetition ratescontinuously adjustable from approximately 1 pulse per second to greaterthan 200 pulses per second, thus capable of achieving high average powerfrom approximately 100 watts to greater than 100 kW, and capable ofachieving any combination of these parameters from a device packagableinto a volume smaller than heretofore possible for a given set ofrequirements.

The present invention also reduces the cost of the laser over any otherlaser capable of achieving substantially the same performance using anyother approach currently known.

The present invention additionally provides an overall system electricalefficiency higher than any other heretofore achieved when operating athigh average power levels; i.e., at 1 kW average or above, while meetinga variety of performance conditions, for example, but not limited to,those given herein.

In one embodiment of the invention, lasers comprising means to extractradiation from the CO₂ molecule are used; however, alternativeembodiments optionally apply generally to NO₂, CO or any gas lasersystem where large-volume, uniform, plasma excitation is used and wherethe gas temperature must be held below values easily achievablecommensurate with applying large quantities of specific energy to thegas (A. E. Hill, Multi-joule pulses from CO₂ lasers: Applied PhysicsLetters, v. 12, no. 9, May 1, 1968).

According to various embodiments, suitably low temperatures aremaintained by forcing gas through plasma excitation regions at high flowvelocities (A. E. Hill, Role of thermal effects and fast-flow powerscaling techniques in CO₂—H₂—He lasers: Applied Physics Letters, v. 16,no. 11, Jun. 1, 1970 ; A. E. Hill, Uniform electrical excitation oflarge-volume, high-pressure, near-sonic CO₂—H₂—He flowstreams: AppliedPhysics Letters, v. 18, no. 5, Mar. 1, 1970; and A. E. Hill, Uniformelectrical excitation of large-volume, high-pressure gases withapplication to laser technology: AIAA 9th Aerospace Sciences Meeting#71–65, New York, Jan. 25–27, 1971). For the case of continuous lasers,gas circulation is optionally achieved by moving the gas through only asmall pressure drop, which is relatively easy to accomplish. Accordingto one embodiment, heat due to wasted energy consumed by the electricaldischarge that excites the laser is removed by heat exchangers prior toreintroducing the gas within a closed-cycle flow loop back into thelaser excitation region. In a variety of embodiments, e.g., for the caseof continuous power extraction, only modest gas pressures (on the orderof several tens of torr) are needed to produce even high powers (10's ofkW), since the lasing molecule is “lased” multiple times in a singlepass through the excitation region (which typically comprises an opticalcavity). Furthermore, due to low pressure, it is relatively easier tocause the discharge (plasma) to occupy a sufficiently large volumeneeded to extract a high power laser mode (or modes).

To extract high average power from a rapidly pulsed laser, the taskbecomes much harder, owing to two primary differences:

-   -   (1) The gas pressure must be much higher in order to store a        large quantity of available power extractable with only one (or        relatively few) recycles of the lasing molecule during a single        pulse; i.e., during a single cavity volume exchange period; and    -   (2) A very large amount of energy must be applied to the plasma        within a transient time period—an operation that is        thermodynamically adiabatic.

The result of (1) is that the plasma does not fill the necessary modevolume uniformly—if at all—without resorting to extreme methods ofplasma excitation. According to various embodiments, the presentinvention specifically provides a method by means of a superiorapproach.

The result of (2) is that the waste energy (that which is imparted tothe plasma but not extracted as laser light) manifests itself as anacoustic shock wave in addition to creating heat. Both heat and acousticenergy must be substantially removed (ideally completely removed)between pulses, a task that typically becomes more severe as the pulserepetition rate is increased.

Heretofore acoustic energy was removed either by means of an extensivearray of passive acoustic absorbent baffles and/or by localizing theshock wave to a small volume region by restricting the flow with orificeplates or gas dynamic nozzles. The end result was that either the lasersystem had to occupy a very large volume, and/or that the pump needed torecycle the gas (called the “prime mover”) had to be very powerful inorder to move the gas through a large pressure drop created by orifices.This resulted in a device that was expensive, energy-inefficient, andlarge. It also added many kW of heat to the gas, which had to be removedin addition to the plasma's waste heat. Generally this prior artapproach doubled the total power requirement of the laser system, aswell as its cost.

According to various embodiments, laser apparatuses of the presentinvention provide a novel means of moving the gas and absorbing theacoustic shock energy which neither necessitates a large gas volume norcreates a substantial pressure drop. Further, according to variousembodiments, apparatuses of the present invention provide for removal ofheat created by the plasma that is compatible with the other apparatuscomponents, enabling the total effect as described. Taken together,these advancements revolutionize the capability, flexibility, costeffectiveness, and size reduction of a multi-megawatt peak-high,rep-rate, multi-kW, average, molecular, gas laser.

Method of Gas Cavity Exchange, Cooling, and Acoustic Abatement

According to an embodiment of the present invention, the usual method ofcontinuously pumping the laser gas flowstream in closed cycle throughthe cavity followed by heat exchangers is replaced by a processcomprising at least two reciprocating steps. This process is brieflydescribed here and in more detail below. Referring to FIG. 1, a laserembodiment of the present invention 2100 is shown. Note that the lasingmode volume 2110 is bounded by special field-shaping electrodes (top2120 and bottom 2150) which form the electrical discharge, and isbounded to the left and right by a dielectric (essentiallynon-conducting) heat exchanger 2160, 2160′ which protrudes nearly intocontact with the plasma volume on either side. Progressing outward,porous-structured catalytic converters 2170, 2170′ follow directlybehind each dielectric heat exchanger 2160, 2160′. The loop is continuedon either side by flow ducts at approximately right angles to thedischarge channel, and are bridged by cylinders completing two opposingclosed paths, referred to as “flow corridors” 2210, 2210′. These paths,however, are blocked by the at least two “loudspeaker” (like) drivers2230, 2230′ (linear motors connected to pistons) positioned back-to-backsymmetrically about the center of the apparatus. Additionally, alabyrinth surrounded by acoustic “absorber structures,” 2220 forexample, but not limited to, structures comprising a Teflon “chips”filling, is positioned into the side flow ducts and woven into the spacebetween the back-to-back drivers. FIGS. 1, 2, and 3 show three differentviews of this particular embodiment as described below.

Referring to FIG. 1, a schematic end view of a laser apparatus of anembodiment of the present invention is shown 2100. A plasma volume andactive laser gain region 2110 is positioned centrally between twosubstantially symmetrical flow corridors 2210, 2210′. The laser gainregion is further positioned between two electrodes, e.g., afield-contoured cathode 2120 and a field-contoured anode 2150. Theelectrodes, as shown, are connected to a plurality of parallel “hybrid”pulse drive coax cables 2250, 2250′ and positioned on a rectangulardielectric flow channel 2180. Note that the field-contoured anode 2120further comprises an X-ray window. The X-ray window allows for theintroduction of X-rays produced by a broad area electron gun (or gunmodules) 2140 aimed at an X-ray target and scatterer 2130. High voltagepulse drive coax cables are suitable for supplying power to the powerelectron gun (or gun modules) 2140.

The two substantially symmetrical flow corridors 2210, 2210′ form anupside-down U-shaped flow path in the laser apparatus. In thisparticular embodiment, two dielectric heat exchangers (e.g., boronnitride dielectric) 2160, 2160′ are positioned in the flow path, one oneither side of the laser gain region 2110 (of course, one heat exchangerhaving two heat exchange regions is within the scope of the presentinvention). Further bounding the laser gain region 2110, are porousstructured, catalytic converters 2170, 2170′ through which the gasflows. Past the catalytic converters 2170, 2170′, the flow corridors2210, 2210′ turn downward forming substantially symmetrical downwardlegs 2211, 2211′. The downward legs 2211, 2211′ are positioned onopposing sides of an acoustic chamber 2212 and comprise rectangularmetal flow ducts 2190, 2190′ (see also, e.g., FIG. 3), which arereinforced with mechanical support ribs 2270, 2270′. The acousticchamber 2212 comprises at least one cylindrical metal speaker driverhousing 2200 for mounting at least two loudspeaker flow reciprocators2230, 2230′ (e.g., linear motors connected to pistons) thereto. Thespeaker driver housing 2200 further comprises, for example, anexternally wrapped acoustic damping blanket. As shown in FIG. 1, theflow reciprocators 2230, 2230′ comprise planar honeycomb loudspeakerdriver diaphragms 2240, 2240′ and the acoustic chamber 2212 furthercomprises acoustical absorber structures 2220 that comprise, forexample, but not limited to, TEFLON chips. Note that additionalacoustical absorber structures 2220 are also positioned throughout theapparatus, primarily along exterior walls of a low pressure enclosure2310.

A schematic side view of the embodiment of FIG. 1 is shown in FIG. 2.This schematic side view shows a variety of components not described inFIG. 1. For example, a cavity mirror 2280, a cavity output coupler 2290,and a dielectric spacer and mode aperture 2300 are shown. This side viewfurther shows nine electron gun modules 2140 and four speakerassemblies, each comprising a driver housing 2210, flow reciprocators2230, and a driver diaphragm 2240. While nine electron guns and fourspeaker assemblies are shown, other combinations and equivalents thereofare within the scope of the present invention.

A schematic top view of the embodiment of FIG. 1 and FIG. 2 is shown inFIG. 3. This schematic top view, in combination with the views of FIGS.1 and 2, allows one of ordinary skill in the art to appreciate theaspect ratios of various structures, according to this particularembodiment. Of course, other configurations, aspect ratios, etc., arewithin the scope of the present invention.

Descriptions of two embodiments of the present invention, referred toherein as Case I and Case II, respectively, follow. According to theseembodiments, each case comprises approximately at least three successivesteps.

Case I: Gas Expansion Followed by “Loudspeaker” Assist.

According to the embodiment of Case I, initially, the speaker driversare positioned to their limit towards one side—e.g., the left side—andare momentarily stationary. Next, the laser discharge is fired. Theresultant laser beam is formed, extracted, and the post-plasma gasvolume doubles in temperature from its initial state (near roomtemperature for the case of CO₂). A shock wave emerges from thistransiently heated volume, but the laser pulse is extracted before theacoustic disturbance develops. This disturbance, however, in someinstances, can ruin the next laser pulse phase integrity if it is notsufficiently dispersed before the next pulse occurs.

Next, the shock is harnessed to provide the first of two coolingoperations. Specifically, the expansion (soon to “shock” down tosubsonic flow) drives much of the hot gas outward uniformly to the leftand to the right into the adjacent heat exchangers. This process happensvery quickly compared to the interpulse time, allowing the coolingprocess to begin.

The expansion waves propagate down through the ducts and impingesubstantially simultaneously from opposite directions onto the speakerdrivers where they are mostly absorbed, thus generating approximatelyequal and approximately opposite electrical pulses across each drivers'“voice” coil. A resistor (matched approximately to the net impedance ofthe drivers) soaks up this electrical pulse, thus dissipating most ofthe lower frequency content of the acoustic wave. Higher frequencycomponents (containing far less energy) may still persist, and these areabsorbed by the anechoic wedges and sidewalls. Multiple reflectionsabsorb diminishingly small remnants of the shock expansion. Dimensionsare small such that adequate acoustic loss (approximately 50 dBattenuation needed per pulse) affords operation up to approximately 200pulse per second repetition rate for a laser that is sized to produce,for example, but not limited to, approximately 5 kW average.

The initial shock cooling is helpful, but in most circumstances notfully adequate to achieve maximum performance. Thus, the loudspeakerdrivers optionally serve a second function: that of further cooling thegas. To accomplish this second function, an electrical drive signal isapplied to all “voice coils” in unison and in phase to push the gas inone direction (no longer bilaterally symmetric) from the cavity andthrough one of the heat exchangers and catalytic converters, where it isto be cooled awaiting the next pulse. The gas reentering the cavity fromthe other side has been pre-cooled since the time of the previous pulseoccurred. The audio-drive signals are synchronized in order to havemoved all drivers to the extreme opposite lateral extent in time toreceive the next pulse, wherein the direction of speaker-driven flowreverses. Audio-drive signals and laser-pulse synchronization are, forexample, automatically electronically controlled and may be variedcontinuously at will.

The functions of both gas pumping and acoustic abatement of multiplereflections can occur simultaneously with the speaker operating both asgenerator and motor. This is possible because the left-hand andright-hand drivers are electrically driven in phase to produce a netmotion in a given direction, but act 180° out of phase as generatorswhen impacted by an acoustic wave. Hence, the dissipation resistor,which is connected to absorb acoustically generated pulses as additive,will not contribute to loading of the audio-drive signal which is phasedto cancel across said resistor (see FIG. 4).

In FIG. 4, a schematic for a combination gas reciprocator and acousticaldamper driver circuit 2400 is shown, suitable for use with theembodiment shown in FIGS. 1 through 3. A cross-sectional view of acylindrical acoustical speaker assembly 2410 is shown near the top ofFIG. 4. The assembly 2410 comprises opposing driver pairs 2412, 2412′,which comprise diaphragms 2414, 2414′ and a pair of opposing drivercircuits 2416, 2416′. Note that the circuits have opposite polarity, thecircuit on the left 2416 has “−” to ground while the circuit on theright 2416′ has “+” to ground.

Referring to FIG. 4, the circuits are connected by a resistor 2418,which has a resistance that is approximately equal to the sum of theimpedance of the drivers. While only two opposing drivers are shown inFIG. 4, this or other circuits are suitable for driving more than twodrivers, e.g., to drive the driver array of FIGS. 1 through 3. Eachcircuit 2416, 2416′ is driven by a power amplifier 2420, 2420′. Thepower amplifiers are driven by a waveform generator 2430, which accepts,for example, input from a timing circuit 2440. The waveform generator2430 produces, for example, a variety of waveforms, two of which areshown in plots in FIG. 4 as Case I and Case II. Case I, as describedherein, comprises a process wherein gas expansion is followed byloudspeaker assist and Case II, as described herein, comprises a processwherein gas expansion is coincident with loudspeaker assist. The timingcircuit 2440 comprises an output for firing the laser and an input, suchas, but not limited to, providing pulse repetition information from,e.g., a scanner, a repetition pulse generator and/or a manual event.

Case II: Gas Expansion Coincident with “Loudspeaker” Assist.

In another embodiment, laser operation comprises a speaker-driven,gas-flow stream that is coincident with the plasma-shock expansion suchthat the shock tends to drive the flow mostly in the same direction asits pre-existing motion, as a single event. The method of thisembodiment invokes a gas dynamic principle know as Raleigh heating,wherein gas already in motion at a relatively high velocity (within thecompressible flow range) will further accelerate the flow in that samedirection. If the initial velocity exceeds approximately Mach 0.4 toapproximately Mach 0.5, the expansion of the plasma can be harnessed tocontribute an ever-increasing fraction of its energy toward furtheraccelerating the gas as its initial velocity is increased. Under suchcircumstances, the heat exchanger may offer more flow resistance as theinitial flow velocity is increased. However, in this scheme, asubstantially intense, substantially sharp-leading edge is applied tothe speaker-drive waveform is used to circumvent this issue. In sodoing, more energy is required to reach the necessary extended velocitydue to increased pressure drop, but this transient segment of the waveform is, for example, short—only a small fraction of one pump-cycletime. When the driver reaches peak velocity, the laser is then pulsedand the drive flow and expansion velocities are (mostly) additive, butin a non-linear fashion (FIG. 5). With each succeeding pulse, the flowstream reverses, as before. In FIG. 5, Rayleigh heating curves are shownplotted as thermal exit Mach number versus specific power load in kW perlb per second.

Detailed theoretical calculations and experimental data are used toconfirm whether the embodiment of Case I or of Case II (or yet anotheralternative embodiment) works best for any given application. From atheoretical point of view, the first scheme is more straightforward.

For both Case I and Case II, the volume of gas trapped between eachspeaker pair transmits force, thus effectively coupling the drivers sothat they share in doing the work of reciprocating the lasing gas mediathrough the cavity.

Also for both Cases I and II, the driver signals are synchronized to thelaser pulse rate according to the requirements for either case by meansof the electronic circuit outlined in FIG. 4. The circuit affordsreal-time variation of the pulse repetition rate—either under manual orautomatic control. For example, in the case of selective layer removal(i.e., paint), the repetition rate can be automatically tied to the scanvelocity of the laser beam at the point of surface interaction, which inturn may be either manually or machine controlled. The benefit is thatthermal damage to the substrate can be automatically eliminated.Moreover, the damage to the substrate may be eliminated by blocking outlaser pulses wherever the substrate surface has been reached. Thesurface status is being monitored in real time by instruments thatmeasure either color or spectral content of the laser plumb.

Plasma Formation and Control

This invention incorporates a special means of forming, pumping, andcontrolling a plasma which provides the laser gain media. It is based inpart on a controlled avalanche process (see, e.g., A. E. Hill,Continuous uniform excitation of medium-pressure CO₂ laser plasmas bymeans of controlled avalanche ionization: Applied Physics Letters, v.22, no. 12, Jun. 15, 1973) but specifically comprises, in oneembodiment, for example, an inventive four-step process shown to yield afactor of two higher specific power loading and much greater range ofapplicability over any other known schemes using the ControlledAvalanche Process. Consider for example, a CO₂ laser embodiment thatproduces approximately 50 joule pulses of approximately 1.4 microsecondsduration and operates at a sustained pulse rate of approximately 200pulses per second. According to this embodiment, approximately 36megawatts pulsed at approximately 10,000 watts average power results foran active cavity volume having dimensions of approximately 2″×2″×30″.There is no other laser known that approaches such levels ofperformance.

Briefly, the Controlled Avalanche Process is, in a manner, somewhatsimilar to an E-beam ionization scheme (see, e.g., K. Boyer, C.Fenstermacher, W. Leland, and M. Nutter, Electron-beam-controlledelectrical discharge as a method of pumping large volumes of CO₂ lasermedia at high pressure: Applied Physics Letters, v. 20, January, 1972)because the Controlled Avalanche Process permits independence ofionization and pump mechanisms, and also their associated E-fieldparameters. Therefore, a relatively large density of “cold” electronsmay be supplied, which are subsequently conducted by application of anelectric field whose magnitude is too low to sustain a normal glowdischarge (i.e., to create ionization of its own accord). However,instead, the Controlled Avalanche Process serves only to pump the lasertransitions by sustaining the electron bath at a low-lying, but optimal,mean temperature for exciting vibrational transitions. Since theionization phenomenon is no longer associated with this pump E-field,the E-field may be tuned at will to optimize the excitation to anymolecular state of any particular molecule. There are many situationswhere the net efficiency for pumping laser levels (or vibrationaltransfer levels) occurs when the pump E-field lies below that levelneeded to sustain ionization. Furthermore, this condition providesuniform stable excitation of very large volumes of high-pressure gaswithout arcing.

It should be noted that, while the electron-beam, ionized,sub-breakdown, field-plasma, formation schemes behave like and exhibitthe same favorable characteristics as the Controlled Avalanche basedscheme described herein, the E-beam technique is inherently unreliable.For that case, the electrons must pass from an evacuated acceleratorregion through thin foil windows into the medium (or high) pressurelaser cavity. This window is blasted by shock waves as the heated laserplasma expands, and it is also subject to puncture by accidental cavityarcs. This arcing behavior can happen often and without warning, causingsignificant damage to the equipment and disruption of, for example, anindustrial process.

A plasma generator embodiment, described herein, comprises a broad areapulsed X-ray source, two electrodes shaped to prevent field enhancement(such as Rogowsky contouring) and one of which contains an X-raytransmitting window (most ideally made of beryllium), a high voltagepulser to drive the X-ray gun, and a special “hybrid” pulser connectedacross the electrodes which serves to generate a multi-component pulseto be described. According to this embodiment, the “hybrid” pulser is anapparatus which generates a string of pulses, each comprising a verysharp, narrow, ultra-high, voltage transient, its leading edge followedby a longer, lower-voltage, flat wave form. The long pulse part of thiswaveform is derived from a pulse-forming network that can beimpedance-matched to the plasma load. Both components of the pulse areoptionally independently controllable and precisely providedesign-specified parameters.

In one embodiment, a particular four-step process operates as follows:

Step 1: An electron-beam generated, broad-area, X-ray pulse is appliedto the plasma, and is conducted from its source into the laser throughthe X-ray window in the electrode. This generates a uniform bed of seedionization (Ne_(preion)≧10⁷ electrons/cm³) throughout the cavity (anddischarge) region.

Step 2: Following a short delay, the uniformly distributed seedionization is caused to avalanche to the full “working level” electronnumber density Ne according to design (perhaps Ne_(pump)=10¹³ to 10¹⁴electrons/cm³) by means of applying an enormously high voltage pulse ofultra-short duration. The exact height and width of this pulse isapplication-specific, but most likely will fall into the range of 100 KVto 2 MV lasting 5 to 75 nanoseconds. More specifically it provides aninitial open-circuit, reduced-field strength of typically 150 Townsends(Td), which amounts to a factor of ˜3 to 8 times the glow potential fora particular gas mix. The avalanche is completed as the pulsed potentialfalls from its maximum field strength (˜150 Td unloaded) to the loadedvalue of perhaps 75 Td for the case of a CO₂ laser. This field fallsjust below the “sparking” potential, but well above the “normal glow”potential.

Step 3: The second function of the hybrid pulse generator takes over thefinal phase of creating ionization as its applied potential falls fromits pulse-forming network charge voltage to one-half that value as theplasma impedance falls to match the pulse-forming network impedance.

Step 4: The system is designed so that plasma impedance comes into matchwith the pulse-forming network impedance at the particular voltage whichprovides the optimal E/N condition for pumping the laser transition.Since for this condition E/N falls below the glow potential (i.e., doesnot contribute to an ionization avalanche), it may be maintained withoutcausing an arc for a specified period of time. Should the ionizationlevel drop unacceptably for the case where the pulse period is verylong, multiple controlled avalanche pulses may be added to the first oneto sustain ionization in a quasi-continuous mode.

The laser transition is continuously pumped under optimum conditionsuntil terminated by the pulse-forming network. Most typically, the pulsenetwork parameters will be selected to apply the maximum specific powerload afforded by thermal bottlenecking (see, e.g., A. E. Hill, Role ofthermal effects and fast-flow power scaling techniques in CO₂—H₂—Helasers: Applied Physics Letters, v. 16, no. 11, Jun. 1, 1970) subject tothe optimal pump potential and the desired pulse width.

The maximum pulse width is typically limited by the time it takes forthe hot gas to expand into the volume external to the laser cavity. Inturn, this depends, for example, on the size of the cavity. For example,if a cavity were of 10×10 cm cross section, a few tens of microsecondsmay bound an achievable upper limit for pulse width.

The discharge voltage/current characteristics leading to establishmentof the plasma via the four-step process are shown in FIGS. 6A, 6B and6C, explained in more detail below. Any network capable of establishingthis process within the laser plasma load—herein called the “hybridpulser”—is within the scope of the present invention.

FIG. 6A shows a plot of plasma voltage and current waveforms generatedby an ideal matched impedance controlled avalanche driver according toan embodiment of the present invention, voltage and current valuescorrespond to parameters for a 0.5 ATM, 10 liter volume laser with apump current plateau of 12.5 kA and τ of between approximately 100 andapproximately 400 nanoseconds.

FIG. 6B shows a plot of plasma voltage and current waveforms generatedby an actual matched impedance controlled avalanche driver according toan embodiment of the present invention, plasma load is approximately 0.5ATM with a 0.5 liter volume discharge and the upper trace is plottedwith 10 kV per division and the lower trace is plotted with 400 A perdivision, both having a time base of 2 microseconds per division.

FIG. 6C shows a plot of plasma voltage and current waveforms generatedby an actual matched impedance controlled avalanche driver according toan embodiment of the present invention, plasma load is approximately 0.5ATM with a 3 liter plasma volume and the vertical scale is 1200 A perdivision having a time base of 0.5 microseconds per division;

Particular circuits that achieve this process by means of directinteraction with the plasma, i.e., wherein the plasma acts to form acontrolling circuit element of the “hybrid pulser,” are shown in FIG. 7Aand FIG. 7B and are within the scope of the present invention.

FIG. 7A shows a schematic of a “simplified” circuit and FIG. 7B shows aschematic of a more elaborate circuit. The circuits of FIGS. 7A and 7Bboth comprise a pump store pulse forming network (“PFN”) 2710, athyatron switch (or spark gap) 2720, at least one transfer capacitor2730, a transfer conductor 2740, impedance matched PFN transfer cables(also suitable as avalanche pulse forming cables) 2750, a laserdischarge cathode 2760, a laser discharge anode 2770, at least oneoptional snubber circuit 2780, a low inductance current return structure2800, and a switch inductance 2880. Variable resistor and switch 2890models the plasma breakdown and is an equivalent circuit for theelectrical discharge. Additional features shown in FIG. 7B and not inFIG. 7A include, a pulsed X-ray electron gun 2810, an X-ray window 2820,a floating filament supply and grid drive electronics 2830, a fiberoptically coupled fire sync signal 2840, a common mode rejection filter2850, an isolation transformer 2860, and a capacitor charging powersupply (or command charge) 2870.

Referring to FIG. 6A, a lumped or distributed pulse-forming network (orline) is provided to store the energy which excites the laser transitionat (nearly) a constant rate over a specified time. Distributed lines arepreferred when the excitation line is short enough (i.e., designed toprovide a T _(pump) period of approximately a few hundred nanoseconds orless), but may be “lumped” using discrete elements (as shown in FIG. 6)to permit longer pulse lengths (typically 1 to 10 μs). For bestdischarge stability, a single lumped section should not exceed a timeconstant τ_(sect)=√{square root over (LC)}≦200 nanoseconds; the fallpump time period then equals τ_(pump)=2N√{square root over (LC)} where Nis the number of discrete LC sections used. Thus, the total pump periodas well as the total stored energy may be defined by the number ofsections and the total capacitance:

${\Delta\; E} = {\frac{1}{2}{{NCV}_{Charge}^{2}.}}$This quantity of energy is ideally selected to provide the (near)maximum energy allowed by thermal bottlenecking for the case of CO₂lasers.

The inductance L of the line element, together with the values of Cdetermine τ_(pump), but also establish the network impedance

$z_{line} = {\sqrt{\frac{L}{C}}.}$All parameters (including discharge composition and pressure, τ_(pump),C, L, N and Z) are chosen such that Z_(line) will be matched toZ_(plasma) in its final sub-breakdown condition when the lasertransition is being pumped.

According to this embodiment, a desirable arrangement ofZ_(line)=Z_(plasma), provides that it is also true that the line willultimately drive the plasma at one-half its initial charge potential,½V_(charge) and conditions are also arranged so thatV_(pump)=½V_(charge) falls below the glow potential, most optimallyV_(pump)≅⅔V_(glow), (derived from a rigorous kinetics calculationincorporating solutions to the Boltzmann electron energy distributionfunctions) wherein the reduced plasma electric field is ˜25 Td(depending on the gas mix) for the case of CO₂.

Referring to FIG. 6A, it is a fortuitous condition of nature that thesparking potential is on the order of two times the glow potential, or(equivalently) the reduced electric field corresponding to breakdownconditions is on the order of two times the value corresponding to glowconditions. Hence, by choosing V_(pump)<V_(glow), we have also arrangedthat V_(charge)<V_(spark). The PFN may therefore be charged andsustained at V_(charge) without causing an arc if the previously heatedand ionized gas has been removed from the cavity prior to charging thecapacitors. Hence, a “command” charge circuit is to be used, or anappropriate delay must be incorporated in the case of using a RFcapacitor charging circuit.

The pump storage PFN (or PFL) is followed by an intermediate LC section,a low inductance switch (thyatron or spark gap) and a set of parallelcables whose combined impedance Z_(cables)=Z_(pfn). The cables play adual role. First, they serve as part of a circuit which generates theinitial high voltage ionization voltage spike, and like the PFN, thecables interact with the plasma so as to control the collapse of thevoltage spike, thus eliminating spark breakdown. Second, the cablesprovide an impedance matched corridor through which to transfer pumpenergy from the PFN to the plasma, becoming both passive and transparentduring the laser excitation process (i.e., once Z_(plasma)=Z_(cables)).Like elements of the PFN, the cables must be precisely specified as tonumber, impedance, length, and correspondingly, their total capacitance.

Initial voltage spike formation begins when the energy transfer switch(i.e., thyatron) is closed. The intermediate transfer cap C_(t)initially charged to V_(charge) then dumps through the switch, thuscharging the cables. The sum of the cable capacity is selected to bemuch less than C_(t), so that its energy gets resonantly transferred tothe cables through the self-inductance of the switch L_(t), which isminimized. In the limit where C_(t)>>C_(cable), the cables get chargedto nearly double V_(charge). Or, by properly selecting the ratio ofC_(t)/C_(cable), the voltage increase ratio can be selected anywherebetween 1 and nearly 2. The transfer time, τ_(tr) is determined by:

$\tau_{tr} = {\pi\sqrt{\frac{L_{sw}C_{\tau}{\sum\limits_{N}C_{Cables}}}{\left( {C_{\tau} + {\sum\limits_{N}C_{Cables}}} \right)}}}$Ideally, τ_(tr) should fall between 1 and 2 cable transient times τ_(C)where τ_(C)=l√{square root over (L_(c) C_(c))} and L_(C) and C_(C) arethe cable's inductance and capacity per unit length, respectively, and Iis the length. Finally, I is chosen such that the spike rise time,τ_(C), is on the order of avalanche rise time at full breakdownpotential. Hence, upon its arrival the cable pulse is reflected bynearly an open circuit since the plasma ionization only the X-raygenerated pre-ionization level (10⁷ electrons/cm³) is present. Hence,the reflected voltage under open circuit conditions heads toward2×V_(cable) or in turn 2×(nearly 2)×V_(pfn), and V_(pfn)≅2×V_(glow).Hence, the reflected potential is heading toward producing 180 to 200Td; i.e., 6 to 8 times the reduced field strength of V_(pump) which isapproximately 25 Td. As approximately 180 Td is approached, theavalanche breakdown accelerates, and the reflected potential getsreduced because the plasma impedance is becoming reduced, according tothe reflection coefficient; i.e.,

$V = {{V_{Cable}\left( {1 + \left( \frac{Z_{Cable} - Z_{Plasma}}{Z_{Cable} + Z_{Plasma}} \right)^{2}} \right)}.}$It is furthermore possible to balance the selection of all parameters,particularly including the level of overvoltage achieveable at the pointof avalanche onset such that the electron number density can bedetermined. The number density is, in fact, determined such that whenthe discharge potential has fallen to V_(pump), then n_(e) has fallen toa value which establishes the discharge impedance which matches Z_(pfn),and Z_(cable). Then: j=n_(e(τ))ευ_(d) and ∫∫n_(e(τ))ευ_(d)dA=σ{rightarrow over (E)}_(pump), which in turn establishes:

$Z_{Plasma} = \left\langle \frac{l_{d}}{\sigma_{\tau}A} \right\rangle$where:

-   -   υ_(d)=electron drift velocity    -   ε=1.6×10¹⁹ Coulombs/electron    -   A=net discharge area    -   l_(d)=discharge length    -   σ=plasma conductivity

In order to match all of these parameters, it may be necessary to addone additional controlling circuit (but not in all cases). Theadditional control can be added by the RC network identified as the“snubber circuit” on FIG. 7. This small capacitive load can be used toreduce and fine tune the maximum potential reached prior to avalanchewithout affecting any other parameters.

When the cables run out of stored energy, they become an impedancematched line which connects the pump storage PFN to its Z-matched plasmaload. The plasma now sees the V_(pfn), which is near V_(spark) and nowreadily conducts current at this potential since it is highly ionized.The ionization density continues to grow so V_(plasma) continues to dropuntil the plateau V_(plasma)=V_(glow) is reached. At this point,ionization losses due to recombination plus 3-body attachment exactlyequal the volume ionization production rate, and could stabilize.However, we have it arranged so that Z_(pfn) balances Z_(plasma) at asomewhat lower voltage, V_(pump), which is completely stable sinceionization is being lost, not gained, and simultaneously the laserexcitation process is near optimal.

Since the PFN (or PFL) is perfectly matched at V_(pump)=½V_(charge) andZ_(pfn)=Z_(plasma), the line simply deposits its energy in a constant orslightly rippled fashion owing to lumped elements until it runs out ofenergy and stops abruptly at time τ_(b)=2N (i.e., the double transversetime for the network).

One more matching condition must be met, namely that intermediatecapacitor C_(t) was chosen to establish the correct cable voltagetransfer, and having done this, the inductor L_(t)C_(t) must be chosento preserve Z_(line)=Z_(LtCt) for that L_(t)C_(t) pair. The L_(t) inturn restricts that charge transfer coming only from C_(t).

Now that all parameters are properly selected we have energy balancecondition:

${\int_{\tau}{\left\lbrack {\int{{{\overset{\rightarrow}{E}}_{\tau} \cdot {\mathbb{d}l}}{\int{\int{j_{\tau} \cdot {\mathbb{d}A}}}}}} \right\rbrack{\mathbb{d}\tau}}} = {\frac{1}{2}{{NC}\left( \frac{V_{Charge}}{2} \right)}^{2}}$All discharge processes are, in turn, controlled by the ionization rateequation:

$\frac{\mathbb{d}n_{ɛ}}{\mathbb{d}\tau} = {S + {\left( {\alpha_{\tau{({E/P})}} - \alpha_{a{({E/P})}}} \right)\upsilon_{d{({E/P})}}{Pn}_{ɛ}} - {\alpha_{r{({E/P})}}n_{ɛ}^{2}}}$where, n_(ε)=electron number density, cm⁻³

-   -   S=external ionization sources (X-ray production rate)    -   α_(τ(E/P))=reduced Townsend ionization coefficient    -   α_(a(E/P))=reduced Townsend 2-body attachment coefficient    -   υ_(d(E/P))=electron drift velocity, cm/sec    -   α_(r(E/P, P))=3-body recombination coefficient    -   P=pressure, torr

The coefficients α_(τ(E/P)), α_(a(E/P)), α_(r(E/P, P)) and υ_(d(E/P))are all calculated by means of solving the Boltzman electron energydistribution equation for incremental values of E/N, or T_(d), which inturn is time dependent.

The network described and drawn in FIG. 7 accurately produces theconditions illustrated in FIG. 6 and in practice it has produced CO₂laser plasmas of an unprecedented quality and power loading. Actualcurrent-voltage characteristics for two different sized lasers are shownin FIGS. 6B and 6C, both of which correspond well with the idealizedtheoretical representation of FIG. 6A.

Applications of the Invention

Various embodiments of the present invention are suitable for use inservicing and/or cleaning of radioactive contaminated surfaces (e.g.,buildings, floors, walls, ceiling, surfaces of equipment, such asgloves, boxes, tanks, machinery (painted or unpainted)). Variousembodiments are suitable for use in the aircraft industry, for example,but not limited to, to remove paint from aluminum and composite aircraftskins, helicopter rotors, radomes, other piece parts, and differentiallycontrolled layer removal from Stealth Aircraft surfaces. Variousembodiments are suitable for removing paint without primer removal, etc.In the marine industry, various embodiments are suitable for surfacepaint/corrosion removal from ships and barges and/or special rubber-likesurface removal from submarines. Also included are operations foroff-shore structures, such as oil rigs, etc.

In the construction industry, various embodiments are suitable forlead-based paint removal from buildings—all surfaces, including woodbuildings. With proper operation, the laser will not start fire andprovides complete containment of lead contaminated debris. According tovarious embodiments, lasers of the present invention are suitable foruse on bridges, water (or other) outdoor storage tanks and even roadtexturing.

In the automotive industry, various embodiments are suitable for use ontrucks, cars, and all heavy equipment. Further applications includedegreasing during fabrication, assembly and paint, coatings and/or waxremoval.

Various embodiments are also suitable for use in the medical industry,including, but not limited to, burn debridement, surgical operations(e.g., skin cancer, blemishes, tumors, etc.), cosmetic surgery (e.g.,wrinkle reduction, hair removal, etc.), surface sterilization of hands,wounds, etc.

Other applications include art restoration and/or graffiti removal(e.g., for paintings, sculptures, graffiti removal from nearly anysurface) and rapid prototyping and/or force free machining. Largerversions of such lasers, are scalable to megawatts average, enabling thefollowing classes of applications: steel industry (e.g., removal ofscale from steel rolls); removal of space debris; meteor deflection(Earth protection); rocket/vehicle propulsion from ground or airbornecraft; and military applications (e.g., target designators, weapons).

The preceding examples can be repeated with similar success bysubstituting the generically or specifically described reactants and/oroperating conditions of this invention for those used in the precedingexamples.

The present invention also pertains to pulse circuits, generationapparatus and methods of generating plasma and/or excited atomicmolecular species, and lasers. The pulse circuits of the presentinvention comprise means for generating ultra-short pulses suitable foruse in lasers. The generation apparatus and methods of the presentinvention comprise means for generating plasma and/or excited atomicmolecular species. For example, various embodiments of the generators ofthe present invention are useful for exciting molecules to excitedatomic states, wherein such molecules include, but are not limited to,oxygen, water, carbon monoxide, carbon dioxide, nitrogen, NO, NO_(x),chlorine, fluorine, bromine, etc. This list is neither exhaustive norexclusive but given to show that the present invention is not limited toexcitation of oxygen molecules. While the embodiments that follow focusprimarily on excitation of oxygen and/or generation of a plasma in thepresence of oxygen, it would be understood by one of ordinary skill inthe art of physical chemistry that the apparatus and methods of thepresent invention are useful for generating plasma and excitingchemicals other than oxygen. Likewise, the pulse circuit of the presentinvention has uses other than for generator apparatus and/or lasers.

Particular embodiments of the present invention pertain to oxygen-iodinelaser systems for use in a variety of industrial applications includingmetal-working applications such as cutting, welding, drilling, andsurface modification. Currently, CO₂ and NdYag type lasers are used forsuch metal-working applications. CO₂ lasers possess good beam quality,high efficiency, scalability to very high power levels (without loss ofbeam quality), and are an economical source of laser power on a per wattbasis; however, they suffer from a long wavelength (10.6 microns) and,therefore, cannot be focused to a tight spot at high power levelswithout causing plasma formation. The long wavelength also preventstransmission via fiber optic cable and limits the ability to cut thicksteel precisely and efficiently. Ultimately, a CO₂ laser cannot cut orweld steel more than a few inches deep. NdYag lasers operate at a muchshorter wavelength, 1.06 microns, which is transmittable via fiber opticcable. The 1.06 micron NdYag wavelength beam, in combination with asuitable lens, allows for beam focusing to a spot area 100 timessmaller, at 100 times greater beam intensity, compared to a 10.6 micronCO₂ wavelength beam. In general, the smaller wavelength beam of theNdYag laser does not cause plasma formation until reaching an intensitylevel that is 100 fold that of the level which causes air breakdown forthe CO₂ laser (i.e., 10⁹ watts/cm² for NdYag verses 10⁷ watts/cm² forCO₂); however, maintenance of beam quality is a major problem of NdYaglasers scaled to a high average power—high power allows for an increasein work process rate. For example, a 2 KW to 3 KW multi-mode NdYag laserproduces a focal spot that is blurred to a 1000 fold greater area thanthat produced by a 60 watt diffraction limited NdYag laser. Increasedfocal spot size also leads to heat loss to the sidewalls of the laser's“keyhole” cut—such heat loss can be a limiting factor in many cuttingapplications.

The oxygen-iodine laser systems of the present invention combineadvantages of CO₂ and NdYag lasers while eliminating many of theirdisadvantages. An oxygen iodine (O₂-I*) laser operates at 1.315 micronsand is thereby transmittable by fiber optic cable. The 1.315 micronwavelength allows for beam focusing characteristic of NdYag lasersoperated below 60 watts average power. Likewise, the O₂-I* laserachieves an intensity of nearly 10⁹ watts/cm² without causing plasmaformation or losing beam quality. Essentially, the O₂-I* laser isscalable to tens or hundreds of kilowatts—megawatts for thatmatter—without loosing beam quality. This allows for a sharp focus athigh power. For example, O₂-I* laser systems of the present inventioncan cut easily through 12 inch-thick steel because such systems delivera power density that is orders of magnitude higher than the rate atwhich the steel absorbs energy through the keyhole walls. A moredetailed description of O₂-I* laser systems of the present inventionfollows.

O₂-I* laser systems of the present invention deviate from traditionalchemical O₂-I* laser systems (COIL systems). Traditional COIL systemsrequire liquid chlorine, concentrated hydrogen peroxide, and potassiumhydroxide. During operation, these chemicals are provided at asubstantial rate and mixed to form a chemical reaction that producesoxygen in a particular excited state called O₂ ¹Δ (O-2 singlet delta).In COIL systems, a flowstream of O₂ ¹Δ passes through a chilled heatexchanger to remove water vapor—an unwanted by-product of the chemicalreaction. Next, the O₂ ¹Δ flowstream passes through a block of heliumand iodine injection nozzles, then supersonic expansion nozzles thataccelerate and cool the oxygen/helium/iodine stream to about Mach 2.8and about 100 K. The 12, which may be carried in buffer gas (e.g.,helium), is generally mixed into the O₂ and O₂ ¹Δ flowstream justupstream of the supersonic expansion nozzles.

During this process, I₂ molecules collide with O₂ ¹Δ and disassociateinto two iodine atoms. The individual iodine atoms, in turn, collidewith additional O₂ ¹Δ molecules whereby energy stored in O₂ ¹Δ moleculesis then transferred to iodine atoms. The transfer of energy causes a“populating” of the iodine's upper laser level. The change in energylevel process is positioned to occur either just upstream of, or within,an optical resonator which is transverse to the supersonic flowstream.The O₂-I* laser beam is produced and directed transverse to thesupersonic flowstream by the optical resonator. The chemical flowstream,post-resonator, passes through a supersonic/subsonic diffuser thatcauses a “shock down” to subsonic flow. The subsonic chemical stream issimply discharged from the system, for example, to the atmosphere,usually with the aid of an ejector pump. The aforementioned COIL systemoperates in an open-cycle configuration because the chemicals passthrough the system only once.

The present invention encompasses both open-cycle and closed-cycleconfigurations; however, as shown below, closed-cycle configurationsimpart substantial benefits to some industrial applications, as dosemi-closed cycle configurations. The present invention allows for asemi closed-cycle operation by virtue of electrical excitation ofoxygen. For purposes of this invention, semi closed-cycle operationmeans that less than approximately 10% of system gas is lost aspercentage of gas flow rate and preferably, this percentage is less thanapproximately 5% while most preferably, this percentage is less thanapproximately 1%. Electrical excitation eliminates the need for liquidchlorine, concentrated hydrogen peroxide, and potassium hydroxide. Inthe preferred embodiments of the present invention, electricity aloneenergizes the laser, transforming pure oxygen into O₂ ¹Δ. Semiclosed-cycle operation of a preferred embodiment of the presentinvention's O₂-I* laser system is illustrated in FIG. 16.

Unlike the COIL system, the closed-cycle operable, electrically drivensystem of the present invention allows for design of practical systemsfor industrial applications. For example, electrically driven O₂-I*systems of the present invention comprise a laser that operates at 1.315microns having the physical size, cost per watt, power scalability, andbeam quality advantages of a closed-cycle, fast-flow CO₂ laser system.

A preferred embodiment of a particular laser system of the presentinvention shares some operational similarities with a United States AirForce COIL system. The Air Force COIL system first provides for I₂collisions with O₂ ¹Δ that disassociate I₂ into 2I and second, providesfor additional iodine collisions with metastable oxygen whereby energyis resonantly transferred to iodine thereby exciting the iodine to theupper laser level. The most significant difference between theaforementioned preferred embodiment and the Air Force COIL system isthat instead of producing the oxygen singlet delta from a chemicalreaction of basic hydrogen peroxide and chlorine, the oxygen singletdelta is produced directly from ground-state oxygen by means of coldplasma electrical excitation.

Normally, the required fractional conversion of oxygen into O₂ ¹Δ cannotbe accomplished by using either conventional (self-sustained) dischargesor microwave discharges, because in both instances heat production isexcessive and limiting, and also the electric field (“E-field”)normalized to plasma density (“E/N”) values encountered are much toohigh. More specifically, E/N is a measure of the E-field normalized tothe plasma density, which plays a controlling role in nearly all plasmaprocesses. E/N is typically measured in Townsends 1 Td (1Townsend)=10–17volt-cm², a value equivalent to 263.9 volts/cm-Amagat. Therefore, aninsufficient fraction of the input energy gets partitioned into thesingle reaction product of importance: O₂ ¹Δ. Chemical kinetics/Boltzmanelectron energy distribution calculations reveal that the necessaryconcentrations of O₂ ¹Δ are generated only if the following (normallymutually exclusive) conditions are simultaneously met:

(1) A high specific energy deposition (approximately 100 KJ/mole O₂)must be applied to a large volume, low pressure (approximately 5 to 50Torr) flowstream of oxygen. For instance, the system requires a volumethat is scalable to produce whatever O₂ ¹Δ flowrate is required for alaser of specific power (e.g., a 100 KW laser might require on the orderof 43 liters of total plasma volume, if operated at 15 Torr totalstagnation pressure);

(2) The energy deposition must occur within approximately 10milliseconds or less (generally due to kinetic losses);

(3) The electric field must be maintained well below the glow potentialso that E/N values lie between approximately 7 and approximately 10Townsends during the entire energy deposition period;

(4) The energy deposition process must be essentially isothermal; i.e.,waste heat must be removed at a rate such that the maximum gastemperature does not build up beyond approximately 200° C.; and

(5) Since self-sustained discharges cannot provide the aforementionedconditions, an external means of ionization must be used. The chosenmethod must not contribute substantially to the net thermal energyinput, nor modify the electron energy distribution substantially overthe drift condition calculated for E/N≅10 Td. Condition (5), as well asthe occurrence attachment instabilities, rule out the use of electronbeam ionization, which otherwise would seem to pose a self-evidentsolution.

The theoretical O₂ ¹Δ yield verses the applied electric field/density,E/N in Townsends (Td), is shown in FIG. 8. Here, the chemical branchingefficiency ratios for all relevant reactions have been calculated forthe electron energy distribution function corresponding to each E/Nvalue. The graph presented in FIG. 8 illustrates that, for E/N fallingbetween 7 and 10 Td, 50% of the applied electrical pump energy isdirectly stored in the O₂ ¹Δ it produces. The graph also shows that atthe electric field necessary to sustain a normal glow discharge (i.e.,E/N=40 Td), the amount of O₂ ¹Δ created is insufficient to sustain laseraction.

In a preferred embodiment, the present invention's method of meeting theaforementioned criteria uses: ultrahigh E/N (initially greater thanapproximately 180 Townsends) and ultrashort (τ is approximately 5–15nanoseconds) pulses at a rep rate sufficient to maintain an averageelectron number density of approximately 10¹³ to approximately 10¹⁴electrons/cm³ during the pump period (typically approximately 20 KHz toapproximately 40 KHz), while maintaining a constant DC pump field (ormagnetically induced square wave potential) at a potential required toproduce an E/N value of approximately 10 Td. In most systems of thepresent invention, ultrashort pulses of less than approximately 75nanoseconds are desired while preferably pulses are less thanapproximately 25 nanoseconds and most preferably, pulses are less thanapproximately 15 nanoseconds. Through experimentation and investigationof a large number of generator configurations, preferred configurationscomprise an integral electrical excitation generator and a heatexchanger. These configurations allow isothermal heat addition; i.e.,rapid removal of waste heat is in equilibrium with internal rate of heatproduction. It is noted that the applied pump potential (E/N isapproximately 10 Td) falls far below the electric field required tomaintain ionization; therefore, a continuous sequence of ultra highvoltage (E/N initially greater than or equal to approximately 180 Td),high repetition rate (e.g., 20,000 to 40,000 pps or more) pulses areapplied to renew the ionization lost while the field is being sustainedat only 10 Td (under fully developed equilibrium conditions, forexample). Note that the residual ionization can reduce the E/N levelneeded to renew ionization from levels of approximately 180 Td to levelsless than approximately 180 Td, in some instances, for example, down tolevels of approximately 100 Td or less. These ionization pulses must bearrested to limit each pulse to less than a few tens of nanosecondsduration. Any ionization pulses of order E/N greater than or equal toapproximately 100 Td to approximately 180 Td (depending on the initialionization number density) lasting longer than approximately 75nanoseconds would lead to arc breakdown. Furthermore, ionization pulseslasting longer than a few tens of nanoseconds generate O¹D at aconcentration which tends toward becoming deleterious. Of course theinvention is not limited to the parameters set forth in this particularembodiment, for example, but not limited to, E/N is not limited tovalues given, the pulse length is not limited to the values given, andthe electron number density is not limited to the values given.Furthermore, the invention is not limited to oxygen iodine lasers,because the pulse circuits and generators of the present invention haveother uses as well. Depending on the particular use and configuration ofany particular embodiment, E/N values of 150 Td are within the scope ofthe present invention for over-volting, as well as, for example, but notlimited to, electron number density values from 10¹² to 10¹⁵.

An example of a magnetic induction loop generator is illustrated in FIG.9. As shown in FIG. 9, the generator 100 comprises a loop portion 102and a measurement/gas exit portion 104. The loop portion 102 comprises acore for providing a poler pulse 108, a current probe 110, a core formain power pulses 112, a gas loop 106 surrounded by a coolant shell 120.As depicted, the cores 108, 112 and the current probe surround the gasloop 106. The gas loop 106 further comprises surface indicia, fins,ribs, etc. 122, for increasing heat transfer to the coolant. The coolantshell comprises a coolant inlet 116 and a coolant outlet 118.

While not an essential part of the apparatus, the measurement/gas exitportion 104 comprises a connection 140 to the gas loop 106. Themeasurement/gas exit portion 104 also comprises a block for sensors andmeasurements 142, a gas exit 144, a fiber optic observation and/orcommunication connection 146, electrical leads for a thermocouple orother suitable temperature measurement device 148, and a pressure sensordevice and/or port for measurement of pressure 150. The block 142optionally comprises windows and a sensor volume, such a block is knownto one of ordinary skill in the art. The gas exit 144 optionallycomprises a throttling valve or similar device for controlling gas flow.

In an embodiment of this inventive generator system, a sequence ofionization pulses are magnetically induced into the loop 106 by means ofa METGLAS®) (Allied Signal Inc., Morristown, N.J.) (or ferrite core)transformer 112 or transformers. Another METGLAS®) transformer 108 isused to induce a sub-breakdown potential, square wave into the loop 106.Of course, a “perfect” square wave having instantaneous rise and fall isnot achievable in practice; therefore, it is understood that squarewaves referred to herein have a rise time and a fall time. In thisparticular embodiment of the present invention, each half cycle of thesquare wave is of sufficient duration as to drive a transformer'smagnetic core to near saturation or to saturation. Likewise, the secondhalf-cycle, which is, for example, of equal magnitude and oppositepolarity to the prior half cycle, drives the core to near saturation orto saturation in an opposite manner. The cycling square wave acts toinduce a substantially constant electric pump field (e.g., but notlimited to, approximately 10 Td) for application to the loop to maintainelectrons at their optimal temperature distribution for exciting O₂ intothe desired O₂ ¹Δ state. The fact that the field reverses periodicallywhenever the core 112 reaches near saturation or saturation does notaffect the process because of the relatively short cycling time asevidenced by the duration of the aforementioned ultrashort pulses.

In an embodiment of this particular example of a magnetic induction loopgenerator, as illustrated in FIG. 9, the plasma path length through loop106 comprises a length of approximately 60 cm, a cross-sectional area ofapproximately 0.7 cm² and a volume of approximately 40 cm³. In thisembodiment, the gas flow path through the loop 106 comprises a length ofapproximately 30 cm and a cross-section of approximately 1.4 cm². Inthis embodiment, the exit volume (loop 106 to sensor/measurement block142) comprises a length of approximately 14 cm, a cross-sectional areaof approximately 0.7 cm² and a volume of approximately 23.1 cm³.

Another embodiment of the present invention, more specifically of amagnetic induction loop generator 200, is shown in FIG. 10. This examplecomprises a loop portion 202 and a measurement/gas exit portion 204(used to verify the proof of principle but not essential to thisembodiment of the invention). The measurement/gas exit portion 204comprises the same features as the measurement/gas exit portion 104 ofgenerator 100. Thus, reference to FIG. 9 and its description issuggested for a description of measurement/gas exit portion 204. Theloop portion 202 of the embodiment shown in FIG. 10 differs from theloop portion 102, as shown in FIG. 9, in several ways. Loop portion 202comprises at least one pot core 212 and preferably four pot cores 212,212′, 212″, 212′″. The loop portion 204 also comprises a current probe210 and a core for providing a poker (avalanche) pulse 208. A loop 206passes through the at least one pot core 212 wherein the loop 206 makesat least one turn or winding and preferably approximately threewindings. Gas enters the loop 206 through at least one inlet 214, whichconnects to and/or forms an anode 220. Gas exits the loop through atleast one gas exit 215, which connects to and/or forms a cathode 222. Asshown in FIG. 10, the gas exit 215 comprises a “T” wherein one pathconnects to the measurement/gas exit portion 204 and the other pathexits through a dump valve and/or to a reservoir.

As shown in FIG. 10, this generator system 200 comprises multi-turntransformer windings comprising segments of the loop 206 in series.“Controlled avalanche” pulses are induced in the loop 206 by means of atleast one ferrite pot core transformer segment 212. Again, the system ischaracterized by extremely short ionizing pulses (e.g., approximatelytens of nanoseconds), ultrahigh E-field (e.g., approximately greaterthan or equal to 180 Td), and a delivered repetition rate ofapproximately tens of kilohertz. A sub-breakdown (10 Td) field (acontinuous direct current) is delivered from a cathode 222 on one end ofthe loop to an anode 220 at the other end. In this embodiment, thedirect current (DC) flows in parallel and in the same direction throughtwo current paths (as shown in FIG. 10) of the loop 206 while theionization pulse current flows continuously around the entire loop 206.Again, the DC's E-field is tuned to the resonant-like magnitude (E/Nequals approximately 10 Td) which drives electron excitation of O₂ toform O₂ ¹Δ.

FIG. 11 illustrates an embodiment of the present invention comprising across-sectional view through a cylindrically configuredtransformer-coupled O₂ ¹Δ generator 300. This embodiment comprises asingle ferrite core 302 to transform both a sequence of approximatelygreater than or equal to approximately 150 Td ionization pulses, and asub-breakdown potential, square-wave pump field as described in theembodiment shown in FIG. 10. The ferrite core 302 comprises a coupledloop 304 lined with at least one heat exchanger 306, preferablyelectrically isolated, to efficiently remove the thermal energy createdby the discharge. The generator further comprises a gas inlet 308 and anexit 310 which connects to, for example, a laser channel 312, forproduction of a laser beam 314. This particular embodiment, while shownwith a single core, optionally comprises multiple cores.

A preferred embodiment of the present invention is shown in FIG. 12.FIG. 12 shows a schematic of a two-tube version of a linear-type,DC-pumped O₂ ¹Δ generator. Actual operation of this preferred embodimentresulted in O₂ ¹Δ yields that were more than sufficient for use in anO₂-I* laser system. Of course, the number of tubes used in thisembodiment is adjustable to generate flow rates needed for a particularlaser system. By way of illustration, FIG. 13 a shows a “strawman”apparatus for an O₂ ¹Δ generator configured to power, for example, butnot limited to, a 5 MW continuous laser. Further description of theapparatus FIG. 13 a is given below. FIG. 6 b shows particular dimensionsof an embodiment comprising the configuration shown in FIG. 6 a.

In reference to FIG. 12, this particular generator embodiment 500 of thepresent invention comprises a generator with an integral heat exchanger502. The generator/heat exchanger 502 further comprises, for example,but not limited to, two tubes 506, 506′ housed within a shell 504. Whiletwo tubes are shown this embodiment is not limited to two tubes and, ingeneral, the embodiment comprises at least one tube. In this particularexample, tubes 506, 506′ optionally comprise a length of approximately 1meter, an inner diameter of approximately 1 cm, a material ofconstruction of Be, or other suitable material, and fluting (or othersurface indicia, etc.) on the inside to improve heat transfer.

Referring again to FIG. 12, this embodiment further comprises an O₂inlet 520, optionally comprising a flow rate control mechanism, a Heinlet 530, optionally comprising a flow rate control mechanism, a gascooling bath 540, optionally comprising dry ice and/or alcohol(s), and avacuum pump 550. Of course use of more than one vacuum pump is possibleand, for example, but not limited to, such pump(s) is (are) ratedindividually and/or collectively at a flow rate of approximately 150CFM. The generator 500 further comprises a variety of measurement/sensorports and/or devices, known to one of ordinary skill in the art. Suchports and/or devices are shown generally in FIG. 12 (510, 510′, 510″,510′″) and comprise, for example, but not limited to, ports and/ordevices for measurement and/or sensing of temperature, pressure, opticalproperties, and the like.

FIG. 12 also depicts electronic circuitry 560 for providing pulses. Onetype of pulse is provided through circuitry 564, for example, but notlimited to, a 50 KV pulse from a circuit comprising at least one vacuumtube. In general, circuitry 564 provides a “jump start” pulse. Circuit564 further comprises a power supply 565, for example, but not limitedto, a 50 KV power supply. Circuit 564 optionally comprises a connection566, for example, but not limited to, a fiber optic connection, totiming electronics 568. Of course, “wireless” modes of connection,relying on electromagnetic transmission are also within the scope of thepresent invention. In turn, the timing electronics 568 optionallycomprises a connection to a velonix driver 570. The velonix driveroptionally comprises a connection to another pulse circuit 562. Pulsecircuit 562 provides, for example, but not limited to, an approximately−180 KV pulse with a frequency of approximately 10 to approximately 25KHz that floats approximately 25 KV above ground. Pulse circuit 562optionally comprises a thyratron-based circuit. Power is provided topulse circuit 562 through power supply 572, for example, but not limitedto, a −45 KV power supply. Power from power supply 572 passes throughcommand charger 574. The pulse circuit 562 further optionally comprisesa DC power supply 576, for example, but not limited to, an approximately12 KV to approximately 18 KV DC power supply. According to electroniccircuitry 560, the pulsers 562, 564 further optionally compriseisolation transformers 582, 584. Such transformers 582, 584 optionallycomprise, for example, but not limited to, 50 KV low capacitanceisolation transformers. As shown in FIG. 12, the power supply 565 isconnected to pulser 564 and further connected to ground, through thepower supply and/or through additional circuitry 586, such as, but notlimited to, capacitive and/or resistive circuitry. The power supply 576is connected to pulser 562 and further connected to ground, through thepower supply and/or through additional circuitry 578, 580, such as, butnot limited to, capacitive and/or resistive circuitry.

The embodiment shown in FIG. 12 further optionally comprises plasmadiagnostics, such as, but not limited to, avalanche current, avalanchevoltage, pump current and/or pump voltage. The embodiment shown in FIG.12 further optionally comprises gas diagnostics, such as, but notlimited to, pressure, mixture/composition, flow rates, and/ortemperatures. The embodiment shown in FIG. 12 further optionallycomprises optical diagnostics and/or recorders. An optical diagnosticsport 512 is shown in FIG. 12.

In an experimental apparatus according to this embodiment, a two tubegenerator was used wherein the tubes were submerged in a fluoroinertdielectric liquid bath which was, in turn, maintained at dry icetemperatures, approximately −78.5° C., by means of circulating pumps.Each tube was injected with metastable helium to pre-ionize the gasvolume while a predominantly O₂ flowstream (with some helium) flowedthrough the tubes at approximately Mach 0.3 to approximately Mach 0.5.

Operation of this aforementioned system comprises, for example, but notlimited to, application of up to approximately 180,000 volt pulses ofapproximately 30 nanosecond duration that are generated at the rate ofapproximately 25,000 pulses per second. Application of these pulsescreated ionization of the gas contained in the tubes. Between pulses,the ionization number density fell by about 15% (the percentage fall isdependent on pressure); however, each succeeding pulse compensated forthis loss in number density. The emergent gas flowed through an opticaldiagnostic cell and into a 150 CFM vacuum pump. The ionizing pulse trainfloated on top of a pure DC electric field provided by an approximately3 KV to approximately 5 KV power supply, which produced about 250 mA ofcurrent (average) in each tube. The O₂ ¹Δ yield was spectroscopicallydetermined and exceeded 16% in pressures of several Torr of pure O₂.This particular preferred embodiment is a configuration that provides abasis for additional preferred embodiments of laser systems to bediscussed.

The generation of O₂ ¹Δ, along with other competing processes, has beentheoretically calculated along the length of the tubes subject toexcitation as described above. The graph of the calculation, FIG. 14,shows that under these conditions the tube will generate its maximumyield of O₂ ¹Δ if its length is approximately 42 cm. Beyondapproximately 42 cm, the “pooling” process causes the creation of O₂ ¹Σto dominate. At 42 cm, the theoretical yield Y (fraction O₂ ¹Δ/O₂ ³Σ) isapproximately 29%—a value sufficient to produce superb laserperformance. Under differing conditions the optimal length optionallydiffers; for example, but not limited to, lengths up to and beyondapproximately one meter in length are within the scope of the presentinvention.

Referring to FIG. 13 a, a “strawman” apparatus 600 for a O₂ ¹Δ generatorconfigured to power, for example, but not limited to, a 5 MW continuouslaser. As shown, the strawman apparatus 600 further comprises at leastone individual bank of plasma tubes 602, 602′. The banks furthercomprise plasma tubes 604, 604′ and current returns 606, 606′, 606″,606′″. Surrounding, or spaced between, each bank 602, 602′ is a heatexchange fluid supply 608, 608′, 608″.

In summary, preferred embodiments of the present invention comprise anelectric oxygen iodine laser that comprises a generator for generatingO₂ ¹Δ wherein the O₂ ¹Δ generator comprises:

(1) A means for generating low-level, pre-ionization of at least onechemical species—“pre-ionization means.” In an aforementioned example,metastable helium was generated using an electric dischargepre-ionization generator, thereafter, the metastable helium was injectedinto a flowstream. Other means of achieving pre-ionization include: (a)dielectric barrier discharges; (b) photo-ionization; (c) X-rayionization; (d) electron beam injection; (e) brush-cathode induced“runaway” electrons; (f) microwave; (g) RF induction (capacitively ormagnetically induced); and/or (H) a nuclear radiation source;

(2) A means for sustaining a significant level of quasi-continuousionization, for example, wherein such means comprises generation andapplication of a rapid sequence of ultrashort, ultrahigh voltage pulsesto at least one pre-ionized chemical species—herein referred to as a“pulsing means.” Where means for sustaining comprises ultrashort,ultrahigh voltage pulses, pulse magnitude significantly exceeds the arcpotential required for creation of an avalanche of ionization to adegree (on the order, for example, but not limited to, of approximately10¹² to approximately 10¹⁵ electrons/cm³) while pulse duration issufficiently short as to prevent arc formation and to minimize formationof undesirable excited state oxygen, e.g., the O¹D state. Pulseduration, or pulse length, is preferably less than a few tens ofnanoseconds, and in all instances, less than approximately 75nanoseconds, and most preferably less than approximately 15 nanoseconds.In addition the pulse energy is capable of “over-volting” the plasma inits original pre-ionized state to typically an initial E/N of, forexample, but not limited to, approximately 150 Td to approximately 180Td. Following the initial ionization pulse of E/N equal to, for example,but not limited to, approximately 150 Td to approximately 180 Td,subsequent ionization pulses taper off to a lower E/N value of E/N equalto approximately 100 Td to approximately 120 Td in response to anincreasing value of electron number density. As a result, the intendedaverage quasi-continuous number density (approximately 10¹² to 10¹⁵electrons/cm³) is controlled and maintained. The pulser circuit isespecially designed to provide the initial 180 Td “jump starter” pulse,then fall off to a suitable, maintained E/N value by means of aninteraction between the circuit and the plasma's conductivity whichcontrols the process. Other comparatively short, “over-volted” forms ofelectrical excitation such as, but not limited to, microwave or RFbursts, may be used as alternatives to or in combination with otherpulsing means and/or other sustaining means;

(3) A means of impressing a sub-breakdown voltage of controlled averagemagnitude or magnitudes. According to the present invention, means ofimpressing causes current to flow through a region of fluctuatingionization as created by the means for sustaining comprising, forexample, the aforementioned pulsing means. Alternatively, asub-breakdown voltage is magnetically induced as, for example,application of aforementioned square wave energy to maintain anapproximately fixed potential through a square wave having alternatingpolarity. The potential, in either instance, is selected so that E/Nfalls well below the glow potential and preferably within the range ofapproximately 7 Td to approximately 10 Td, of course this value isadjustable to account for other system parameters. In preferredembodiments using a controlled “graded” E/N, E/N is continuously variedalong the operational path and is a function of O₂ ¹Δ concentration (orO₂ ¹Δ pressure). Several preferred embodiments of the present inventionuse graded E/N technology. Grading of E/N over system operation allowsfor, in most instances, optimum efficiency. As mentioned previously, andwith reference to FIG. 8, choice of E/N depends on levels of O₂ ¹Δ,whether measured in terms of concentration or pressure. In particular,O₂ ¹Δ levels are monitored (primarily for experimentation) withreference to concentrations and pressures of other chemical specieswithin the system, for example, but not limited to, other oxygenspecies.

(4) A means of exchanging heat energy is desirable, and in mostinstances it is required, because the temperature dependence of thepooling rate for O₂ ¹Δ+O₂ ¹Δ→O₂Σ+O₂ ³Σ, and the very strong temperaturedependence of the equilibrium constant for the excitation reaction O₂¹Δ+I→O₂ ³Σ+I*. Thus, it is imperative that the process be kept as coldas possible and occurs as quickly as possible. Within generators of thepresent invention, the aforementioned conditions are met by, forexample, starting the process very cold, removing the generated heatimmediately and flowing the gas through the apparatus as quickly aspossible. Within the lasing volume, fast flow rate and cold temperatureconditions are simultaneously met by expanding the flow to supersonicvelocities.

EXAMPLES

Three specific point design examples of lasers intended for threedistinct classes of applications are presented below. All of theseexamples are based on a linear O₂ ¹Δ generator/integral heat exchangerconcept as illustrated in FIG. 12.

Case I System: Open Cycle, 20 KW Class, Continuous Laser.

This configuration is intended to provide a very compact, light-weightlaser for applications where only short-run times are needed but compactpackaging concerns are at a premium. Typical applications for such lasersystems include fracturing of rocks in mining or well-drillingoperations, where field portability is advantageous. In FIG. 15, bothside view (top drawing) and top view (bottom drawing) of a Case I Systemof the present invention are shown. The top view shows only a laserchannel, which is common to two other configurations that follow (referto FIG. 15 for other cases).

A laser 800 according to a preferred embodiment of the present inventionis shown in FIG. 15 a. This open cycle electric oxygen iodine laser 800comprises an oxygen supply 810, a helium supply 820, an iodine supply830, a power supply system 840, an O₂ ¹Δ electric generator/heat sinkassembly 850, a resonator cavity 860, a supersonic/subsonic diffuserdischarge assembly 870 and a heat exchange system 880.

As shown in FIG. 15, the heat exchange system 880 of this embodimentconnects to the oxygen and helium supplies 810, 820, the O₂ ¹Δ electricgenerator/heat sink assembly 850, and the supersonic/subsonic diffuserdischarge assembly 870. The heat exchange system 880 further comprisesat least one pump for pumping fluid and/or gas 882, 882′, 882″. The atleast one pump provides for circulation of fluid/gas from the O₂ ¹Δelectric generator/heat sink assembly 850 to the heat exchange system880. In this particular embodiment, the heat exchange system 880 furthercomprises, as shown, a heat exchange loop 884 for exchanging heat withan ejector gas from an ejector gas supply 886. This sub-assemblyoptionally comprises, in lieu of or in addition to the heat exchangeloop 884, a thermal energy input 888 to achieve a suitable ejector gastemperature. An ejector gas manifold from the ejector gas supply 886enters the supersonic/subsonic diffuser at a point upstream 874 from thesubsonic portion 876 of the diffuser; however, the ejector gas does notenter the flow stream until approximately the shock region, which issubstantially between the supersonic and subsonic regions (as shown moreclearly in FIG. 15 c below).

The O₂ ¹Δ electric generator/heat sink assembly 850 of this particularembodiment comprises at least two tubes 852, 852′. Located at oppositeends of the tubes 852, 852′ are fore and aft electrodes 854, 854′. Thisparticular embodiment is optionally configured with a fore cathode oranode and an aft anode or cathode, respectively, for purposes ofdischarging a direct or alternating current at sub-breakdown fieldstrength into the plasma. In either instance, metastable helium isformed at or near the fore electrode, for which the fore electrodecomprises a cathode, regardless of whether it comprises a cathode oranode for purposes of providing seed volume ionization from which toinitiate an avalanche. Of course for low pressure operation and othertypes of operation, the invention does not have to rely on thisparticular apparatus or method of forming metastable helium. Othermethods and apparatus for providing seed volume ionization are withinthe scope of the present invention and known to those of ordinary skillin the art.

The power supply system 840 comprises a floating, high repetition,nanosecond, high voltage pulser 842, a DC power supply 844, powerconditioning electronics 846, a high voltage isolated power transformer848, a command charger 847 and appropriate leads 843 to the O₂ ¹Δelectric generator/heat sink assembly 850. The command charger 847 ispositioned between the power conditioning electronics 846 and thefloating, high repetition, nanosecond, high voltage pulser 842. The highvoltage isolated power transformer 848 is connected to the powerconditioning electronics 846.

The laser beam is produced at the resonator 860, which in thisparticular embodiment comprises a two-pass unstable resonator cavity,shown in an end view in FIG. 15. The resonator 860 is positioned afteran iodine injector 832 and before the supersonic diffuser 872. In thisparticular embodiment, the iodine injector 832 comprises a supersonicnozzle block, which a particular embodiment thereof is described infurther detail below.

The iodine injector 832 shown in FIG. 15 a comprises a supersonic nozzleblock. A close-up of this block 900 is shown in FIG. 15 b. This blockcomprises an inlet side 902 and an outlet side 904. Gases in subsonicflow enter the inlet side 902, mix with iodine, and optionally acombination of helium and iodine, supplied through iodine injectionports 903, 903′, in a mixing region 906, 906′, 906″. This mixture ofgases expands in the supersonic expansion region 908, 908′, 908″ toachieve supersonic flow. In a particular embodiment of the invention,gas leaving the supersonic nozzle block comprises a velocity ofapproximately Mach 2.5 to approximately Mach 3.0. The gas furtheroptionally comprises a temperature of approximately 112 K or lower. Thebasic principles of the supersonic nozzle block of FIG. 15 b are knownto those in the art of COIL lasers.

FIG. 15 c shows a top view of the inventive apparatus of FIG. 15 a. Inthis view of this particular laser embodiment 800, the oxygen supply810, the helium supply 820, the iodine supply 830, the O₂ ¹Δ electricgenerator/heat sink assembly 850, the resonator cavity 860, and thesupersonic/subsonic diffuser discharge assembly 870 are shown. Theresonator cavity 860 further comprises a plurality of resonator mirrors862, 862′, 862″, 862′″. The resonator cavity additionally comprises atleast one laser beam output coupler 864. This mirror optionallycomprises an annulus for output of an annular laser beam, if used inconjunction with an unstable resonator, or a partially transmitting andpartially reflecting optical element, if used in conjunction with astable resonator.

In a Case I System, all laser gases pass through the channel only once(open cycle) and must be stored in a quantity sufficient to cover aparticular application or mission. Storage of gases in cryogenic formprovides a means of cooling, or exchanging heat energy, with the systemand, in turn, heat energy absorbed into cryogens causes a change to agaseous state and vaporization.

In a Case I System, a O₂ ¹Δ generator of the present inventionconsisting of, for example, but not limited to, approximately 80 tubes,each approximately 42 cm long (longer tubes, for example, but notlimited to approximately one meter in length or longer are also withinthe scope of the present invention), produces an oxygen flow rate thatis sufficient to power a 20 KW laser. The generator, in turn, comprisesa pre-ionization means and a means for sustaining quasi-continuousionization by the same kind of pulsers and power supplies described forthe 2 tube experimental generator of FIG. 12. The physical operatingconditions for this laser are summarized below.

Physical Operating Conditions for 20 KW Electric Oxygen Iodine Laser

Minimum Yield (Y)=0.16, T_(cav)=112 K Case

Resonator:

-   -   α_(o)=0.0074, Mag=1.4 Resonator, L=3 meters total path    -   Scaled from ROTOCOIL according to:

$\alpha_{o} \approx \left( {1 - {\left( \frac{1}{{2K_{eq}} + 1} \right)\left( \frac{1}{Y} \right)}} \right)$

-   -   Lumped Mirror Losses: r₁,r₂=0.998, |γ|_(max) ²=1−δ≅0.75

$\begin{matrix}{\eta_{ext} = {\eta_{o}\eta_{s}}} \\{= {\frac{\ln\left( {{\gamma }^{2}r_{1}r_{2}} \right)}{2\left\langle {\alpha_{o}L} \right\rangle} + 1 + {\left( {2 - r_{1} - r_{2}} \right) \times \left\lbrack {\frac{1}{\left\langle {2\;\alpha_{o}L} \right\rangle} + \frac{1}{\ln\left( {{\gamma }^{2}r_{1}r_{2}} \right)}} \right\rbrack}}} \\{= 0.92}\end{matrix}$

Kinetics:

$\eta_{kin} = {\frac{Y - \left( \frac{1}{{2K_{eq}} + 1} \right)}{Y} = 0.888}$

-   -   where:

K_(eq) = 0.75 × 𝕖^(402/112) = 27.16$Y = {\frac{\left| {O_{2}^{1}\Delta} \right|}{\left| {O_{2}^{1}\Delta} \middle| {+ \left| {O_{2}^{3}\sum} \right|} \right.} = 0.16}$$\begin{matrix}{{{Power}\mspace{14mu}{Output}} = {20\mspace{14mu}{KW}}} \\{{{Power}\mspace{14mu}{Available}} = {P_{out}/\left( {\eta_{o}\eta_{s}\eta_{pack} \times \eta_{kin}} \right)}} \\{= {20\mspace{11mu}{{KW}/\left( {0.92 \times 0.9 \times 0.888} \right)}}} \\{= {27.2\mspace{14mu}{KW}\mspace{14mu}{Stored}\mspace{14mu}{Power}}}\end{matrix}$$P_{stored} = {{\overset{.}{M}}_{({{moles}/\sec})} \times \left( {Y - \left( \frac{1}{{2K_{eq}} + 1} \right)} \right) \times 91.3\;{KJ}\text{/}{mole}}$$\overset{.}{M} = {\frac{27.2\mspace{11mu}{KW}_{stored}}{\left( {0.16 - 0.018} \right) \times 91.3\;{KJ}\text{/}{mole}} \cong {2.1\mspace{14mu}{moles}\text{/}\sec}}$Summary of 20 KW Laser

Input Parameters:

-   -   M=2.5 Flow    -   T_(cav)=112 K    -   K_(eq)=27.16    -   M≅2.1 mole/s O₂ (+2.1 mole/sHe+0.02−0.04 mole/sI,)    -   P_(gen)≅25 TorrO₂₊₂₅ Torr He    -   P_(cav)≅5 Torn, Total    -   Y=0.16, fraction O₂ ¹Σ=0.018

Output Parameters:

-   -   Power Out=20 KW    -   P_(stored)≅=27.2 KW    -   η_(next)≅0.92    -   η_(pack)≅0.9 (assumed)    -   η_(kin)≅0.888    -   α_(o)≅0.0072    -   Mag 1.4 Res approximately 2 times diffusion limit        Power Requirements

I. Power Required to Drive Laser Plasma Ionization  28 KW Electric PumpExcitation 140 KW Gas Re-Circulation  20 KW Auxiliary Systems  40 KWPower Conditioning Losses (includes electrode losses)  26 KW Laser PowerRequirements, subtotal* 254 KW Laser Wall Plug Efficiency (less coolingsubsystems)   8% II. Power Required to Reject Heat For Closed CycleOperation (if electrically refrigerated) Power Added to Reject 40 KW at+20° C.  40 KW Power Added to Reject 114 KW at −20° C. 130 KW ThermalManagement Subtotal 170 KW Total System wall Plug efficiency(electrically refrigerated) 4.7% *Assumes worst case performanceestimates, and that all heat is exhausted into ambient air (no “coolingtower”). Specifically assumes: Fraction O₂′Δ generated 17.8% FractionO₂′Δ lost to cooling  1.8% Fraction O₂′Δ reaching output of generator  16% Efficiency of O₂′Δ generation at 10.5% concentration   22% Totalkinetic energy in flow stream  30 KW Pump power needed to generate 30 KWexcited species 140 KW Note that “II. Power Required to Reject Heat forClosed Cycle Operation” is also useful in describing open-cycleoperation, wherein dynamic gas expansion from a source to the generatorand/or cryogens are optionally used to maintain temperature. Note thatall of the numbers and calculations shown are for illustration ofvarious embodiments of the present invention and do not limit the scopeof the invention.

As shown, subsequent to the oxygen plus helium (or, e.g., argon) buffergas passing through the O₂ ¹Δ's generator structure, iodine vaporcarried by a buffer gas (e.g., helium) is injected into the flowchannel. Immediately past the mixing region, the flowstream is expandedto a flow velocity of Mach 2.5 where cooling occurs, to approximately112 K at the resonator. The cavity is 1 m wide, utilizes a 2 passtransverse unstable resonator, which produces a 2 timesdiffraction-limited beam at approximately 20 KW. About 200 KW ofelectrical power is supplied to the system, and approximately 2.1 molesO₂ plus approximately 2.1 moles He are stored for each second ofoperation.

Although design calculations were based on 20 KW operation, thetechnology of a Case I System is scalable up or down as needed. In fact,the results presented above were based on O₂ ¹Δ yield measurements thatare approximately a factor of two less than a realistically achievable,optimal yield. Therefore, a most optimistic scenario achieves 40 KWaverage power output from the same Case I System without need forfurther power input.

Case II System: 20 KW Average Power-Class, Closed-Cycle, ContinuouslyOperational Laser.

This system employs the same basic cavity and operational specificationsas a Case I System, except that it operates (nearly) closed cycle, sothat laser gas make-up rates are relatively inconsequential. Thisresponds to the requirements for a typical heavy-metal workingindustrial laser and results in a package which very closely resembles a20 KW, CO₂ laser in terms of efficiency gas make-up and cost per watt;however, a Case II System of the present invention makes much narrowercuts, can cut up to ten times deeper, and nearly ten times faster thanits CO₂ laser counterpart. FIG. 16 illustrates an embodiment of a CaseII System showing how the gas flow loop is nearly closed.

Case II laser systems are truck-mountable and field operational, therebyenabling the disassembly of 12 inch-thick steel nuclear reactor vesselsand centrifuges for which the U.S. Department of Energy has a mostpressing need. Ships, tanks, and many other heavy manufacture operationsare foreseen target users of Case II System embodiments of the presentinvention.

Referring to FIG. 16, a closed-cycle embodiment of a laser system 920 ofthe present invention is shown. This laser system 920 comprises agenerator/heat exchanger 922; a power supply system 924 that comprises afloating, nanosecond, high voltage pulser and a DC power supply; a gasreturn flow loop 930 and an iodine vapor-He return loop 950. The gasreturn flow loop 930 further comprises at least two heat exchangers 932,932′ (optionally comprising a chiller, see element 932′); a roots blower934; a slow flush vacuum pump 936; and a make-up oxygen supply 938. Theiodine vapor-He return loop 950 further comprises a helium supply 952and a heat exchanger 954 that optionally comprises a heater.

Referring again to FIG. 16, a Roots blower pump 934 is used torecompress gases emerging from the subsonic diffuser 960, after whichthe heat introduced by the pump is removed by a heat exchanger 932′, andthe flowstream is reintroduced to the electric O₂ ¹Δ generator 922. Thisparticular Case II System resembles a CO₂ laser system; however, with aunique need for handling recycle of iodine 950. In a preferredembodiment of a Case II System, Iodine vapor (carried by heated helium)must be injected just upstream of the supersonic nozzles 956 and removedfrom the flowstream before the flow reenters the O₂ ¹Δ generator 922.Hence, this particular Case II System requires two separate flow loops930, 950, one for the bulk of the gas and another for a relatively smallamount of iodine (amounting to approximately less than 1% of the netflowstream). Where buffer gas is used, the gas comprises oxygen species,buffer (e.g., He and/or Ar) and iodine species.

In the aforementioned Case II System, gaseous iodine is “frozen out” ona cooled structure, i.e., a condenser/heat exchanger, 932′ downstream ofthe subsonic diffuser 960, as illustrated in FIG. 16. Solid state iodineresides in crystalline form solidified on the condenser's 932′ extensivesurface area. After a period of time, for example, a few hoursoperation, the condenser's surface becomes saturated. The saturatedcondenser surface is then moved into a second position 954 where it isheated thereby subliming and liberating the solidified 12 as vapor,which, in turn, re-enters the mixing nozzles. In preferred embodimentsof a Case II System, there are at least two identical condensers 932′,954, at least one for condensing 12 vapor from the system 932′ and atleast one for subliming 12 solid for re-entry to the system 954 asvapor. As shown in FIG. 16, interchange of surfaces and/or condenserstructures requires a downtime of, for example, a few minutes, everyseveral hours; however, the interchange operation is fully automatable.

Case II Systems, as noted for CO₂ laser systems, do not operate as acompletely closed-cycle: some exchange of gas is required. For Case IISystems, heated helium gas 952 must be injected to carry the iodine anda correspondingly small amount of laser gas must be pumped out of thesystem. This process disturbs the helium/oxygen ratio thereby requiringintroduction of additional “make-up” oxygen 938 to maintain a properbalance. Hence, the system is not completely closed, but the make-uprates are tolerable and practical for the aforementioned applications.

In addition to powering the Roots blower 934, a formidable amount ofenergy must be spent to cool the O₂ ¹Δ generator 922. The power drainattributable to cooling is comparatively negligible because the laserper se is very efficient. For example, refer to the numbers presented inFIG. 14 and above as indicators of the comparative power requirements.Calculations for Case II Systems indicate that an overall efficiency of5% is achievable—an efficiency comparable to that of a CO₂ laser systemwhen one accounts for the costs of gas circulation, laser cooling,chilled water requirements, etc.

Case III: High Repetition, Pulsed, 150 KW Average Power, Approximately200 Joules/Pulse (200 Megawatts Peak), Closed-Cycle Laser.

This particular embodiment of the present invention is intended toaddress applications such as, but not limited to: (1) nudging spacedebris out of orbit so that it burns up in the atmosphere; or nudgingcomets or asteroids repeatedly to gradually divert their path so thatthey miss striking the earth. Scaled-up Case III laser systems couldalso play a role in generating controlled nuclear fusion power orpropelling rockets and/or satellites into space.

For purposes of this discussion, the calculated parameters for a CaseIII System appear below.

150 KW Ave. 200 J/Pulse Closed Cycle Electric Oxygen Iodine Laser

Minimum Yield (Y)=0.16 (assumed), Cavity Mach=2.5, T_(cav)=100 K Case

Resonator:

-   -   α_(o)=0.002,I_(sat)≅1440 W/cm², L=600 cm, folded, Mag=1.4        Resonator    -   α_(o) scaled from ROTOCOIL data according to:

$\alpha_{o} \approx {\left( {1 - {\left( \frac{1}{2K_{eq}} \right) \times \left( \frac{\left| {O_{2}^{3}\sum} \right|}{\left| {O_{2}^{1}\Delta} \right|} \right)}} \right)\frac{Y}{Y_{RC}}}$

-   -   I_(sat) scaled from ROTOCOIL data, according to I_(s)≈ρV_(cav)    -   Lumped Mirror Losses: r₁,r₂=0.998, |γ|_(max) ²=1−δ≈0.75;

$\eta_{ext} = {{\eta_{opt}\eta_{sat}} = {{1 + \frac{\ln\left( \left| \gamma \middle| {}_{2}{r_{1}r_{2}} \right. \right)}{2\left\langle {\alpha_{o}L} \right\rangle} + {\left( {2 - r_{1} - r_{2}} \right) \times \left\lbrack {\frac{1}{\left\langle {2\alpha_{o}L} \right\rangle} + \frac{1}{\ln\left( \left| \gamma \middle| {}_{2}{r_{1}r_{2}} \right. \right)}} \right\rbrack}} = 0.87}}$

Kinetics:

$\eta_{kin} = {{1 - \left( \frac{1}{\left( \frac{O_{2}^{1}\Delta}{{O_{2}{total}} - {O_{2}^{1}\sum}} \right)\left( {{2K_{eq}} + 1} \right)} \right)} = 0.90}$

-   -   where:

${{\overset{.}{M}\left( {Y - {\left( \frac{{O_{2}{total}} - {O_{2}^{1}\sum}}{O_{2}{tot}} \right) \times \left( \frac{1}{{2K_{eq}} + 1} \right)}} \right)} \times 91.7} = {430\mspace{14mu}{KW}}$Continuous Wave Power Available from Flowstream Equals:

${K_{eq} = {{0.75\;{\mathbb{e}}^{\frac{402}{T_{x}}}} = 31}},{T_{c} = {108K}}$

-   -   Sanity Check: ∫∫∫α_(o)I_(sat)dV=696 KW (deviation probably due        to scaling of I_(sat)).        Energy per pulse out=(334        J/pulse)×(η_(opt)η_(sat))×η_(kin)×η_(kin)334×(0.87)×0.9×0.9=235        J/pulse

-   Number Cavity Exchange Rate=1290

-   Maximum Available Power Out=300 KW

-   Practical Available Power:    -   for 2 exchanges per pulse—650 pps=153 KW    -   for 3 exchanges per pulse—430 pps=100 KW        Power Requirements: (33% Duty Cycle)

Electrical Efficiency of Generator 20% Pooling Loss, Efficiency 90%Threshold Efficiency 90% Energy in Flow (100% Duty) 430 KW Pump Power700 KW Continuous Avalanche Pre-Ionization 100 KW Cathode/Anode Loss  15KW Auxiliary Systems  33 KW Prime Mover 380 KW Refrigeration 700 KWPower Conditioning 200 KW Total 2128 KW Prime Mover/Gas Requirements:

approximately 400,000 CFM 10 Torr Inlet δP = 10 Torr O₂ Flow: 32 moles/sHe Flow: 32 moles/s Make up: Plug Efficiency at 3 exchange/pulse:100/2128 = 4.7%

In particular, the feasibility of extracting giant pulses at asufficient rep rate to enable the aforementioned types of applicationsis demonstrated.

A preferred embodiment of a Case III System comprises a closed-cycle,supersonically flowing, cavity configuration incorporating transverseoptical extraction from an “unstable resonator.” This embodimentcomprises continuous pumping from a linear integral heat exchanger O₂ ¹Δgenerator, followed by iodine vapor (plus, e.g., buffer) injection—thensupersonic expansion. Lasing is retarded while excited gas fills thecavity by means of applying a “permanent” magnetic field that causesZeeman-splitting of laser transitions states. Once the cavity is filledand acoustical disturbances have settled out, at least one Helmholz coilis electrically pulsed to nullify the permanent magnetic field. Throughpulsed nullification of the permanent field and the resulting formationof spontaneous noise, the resonator builds a laser beam within severalmicroseconds. Alternatively, a regenerative amplifier replaces theaforementioned unstable resonator. If pre-seeded from a localoscillator, this alternative system will provide much shorter pulses.Gordon D. Hager at Phillips Laboratory, Kirtland Air Force Base, USA,has reduced the Zeeman splitting method of Q-switching to practice. See,e.g., “Demonstration of a repetitively pulsed magnetically gain-switchedchemical oxygen iodine laser,” Hager et al., Chem. Phys. Letters., Vol.204, No. 5, 6, pp. 420–429 (1993). The Zeeman splitting and Q-switchingmethods and apparatuses of Hager are hereby incorporated by reference.

There are some particular constraints that are driven by the nature ofthe technology, and the nature of the mission. For example, the laser'scavity must operate at low temperatures, for example, approximately 100K is a preferred operating temperature, and the cost of conventionalrefrigeration reduces overall economy. Hence, supersonic flow providesthe most practical way of reducing the cavity temperature. Also,hundreds of joules (perhaps kilojoules) must be extracted in each pulse,so the cavity must be large enough to store this energy. A large cavitycombined with supersonic flow translates to seemingly high volumetricflow rates (approximately 480,000 CFM for the case presented); however,the pressure is low and therefore the prime-mover power amounts to amuch smaller fraction of the total system power than normallyencountered with high average power lasers; i.e., only 10% of the totalsystem power is consumed by the prime mover for this “strawman” designif it were to run either CW or at full average power in the pulsed mode.Acoustic settling times may preclude pulsing the flow once per cavityexchange (which would deliver 225 KW average); however, operating at 2to 3 cavity exchanges per pulse maintains an overall efficiency as highas approximately 5.5% or 4.5%, respectively. Under such circumstances,230 joule pulses are extractable from the particular cavity analyzed.

Naturally, if the system is to operate continuously at a repetition ratefalling between 430 and 660 pps, closed-cycle operation is greatlypreferred. And for closed-cycle operation, the most severe energypenalty becomes the matter of removing waste heat. Half of the wasteheat (approximately 1 MW) is efficiently carried off by water at roomtemperature, but an additional approximately 1 MW must be removed atreduced temperatures (−30° F.). Removal of additional waste heat willcost at a minimum 1 MW of electric power to drive, for example, arefrigerative heat exchanger. The remaining thermal task—that ofmaintaining approximately 110° K within the cavity—is accomplished bysupersonic expansion. This thermal energy burden, in addition to theprime-mover power requirements, was included in the derivation of the 5%wall plug efficiency factor. Again, in terms of efficiency, the systemsof the present invention rival CO₂ laser systems.

Regarding yield, or fraction of O₂ ¹Δ, achievable by the lab generatorused in several of the aforementioned examples, lab measurementsindicate a yield of at least approximately 16%—the “strawman” design andcalculations are based on this value. Theoretically, more than twicethis yield is expected (i.e., approximately 32%), and in fact, highyields were measured on several occasions; however, these higher valueswere not measured repeatedly with statistical accuracy in mind.Additionally, a known artifact in lower measurements accounts for thepossible anomaly of low yield measurements. Therefore, operation of thepresent invention can conservatively provide yields of at least 16%.Ultimately, higher yields will have a very positive impact in many ways,resulting in: a smaller system size; a higher pulse energy; a shortercavity resonator for a given power level (owing to higher gain); ahigher efficiency; less severe refrigeration/cooling requirements; andpotentially subsonic operation for certain missions.

The aforementioned “strawman” designs assume that generator pressure isdoubled over the levels demonstrated because it is theoretically andpotentially achievable. If not achievable, the pulsed energy storage ishalved. On the other hand, if the generator pressure is doubled again(which is quite probable), the pulse energy density doubles.

Finally, the prime-mover power requirement was based on an assumeddiffuser recovery factor of 50%. Because there is a small, but yetunquantified, heat release in the supersonic flowstream due to thethermalization of energy stored in O₂ ¹♮, the diffuser operation ispotentially adversely affected. This may potentially double theprime-mover power requirement resulting in an overall efficiencyreduction from approximately 5% to approximately 4%.

Pulser Circuits and Generator Examples

Specifically it is the function of the “controlled avalanche” or pulsercircuit to provide and sustain a quasi-continuous level of ionizationwithin the O₂ ¹Δ generator needed to conduct current during the offperiods between the pulses it generates. Regarding ionization,information disclosed in “Continuous Uniform Excitation of MediumPressure CO₂ Laser Plasma by Means of Controlled Avalanche Ionization,”Alan Hill, Applied Phys. Letters 22(12), 15 Jun. 1973 is relevant tothis point; however, such technology was not previously applied togeneration of atomically excited molecular species. This article isincorporated herein by reference. This current, in turn, is driven bythe application of a second, DC potential (or equivalent) whosemagnitude is of a specified value falling well below that value neededto contribute to the ionization process.

In addition to providing a continuous stream of pulses that sustainionization, it may also provide an associated string of pulses used togenerate pre-ionization or equivalently meta-stable helium in chambersthat lie upstream of the main discharge sections. Such pre-ionizationwould float on top of the primary “controlled avalanche” pulses, withthe controlled avalanche pulses perhaps being delayed slightly withrespect to the pre-ionization pulses. (There are a number of methods,previously outlined, for generating the pre-ionization.)

For the case of the preferred embodiment, the controlled avalanchepulser—together with its pre-ionization complement—floats on top of apure DC potential whose function is to provide the pump current under atemporally steady (although perhaps spatially graded) electric field ofthe order E/N=10 Td.

Finally it is the function of either this pulser or an associated pulserto provide a single, giant pulse at turn-on in order to produce theultimate, quasi-steady-state level within a few pulse periods. Thisone-time intermediate “jump start” process negates the need to supplyevery pulse at an E/N value of approximately 180 Td. Instead, we provideonly the fast pulse at the value of approximately 180 Td, then allow thequasi-continuous pulser circuit to settle down to its ionizationmaintenance level, which under the conditions of residual ionization (atits start) most probably falls between the value E/N=80 Td and E/N=120Td (depending on the design level of electron number density, ionizationrep rate, pressure, and gas mixture).

The pulser's circuit is designed to interact with the plasma'sconductivity, such that its applied potential falls below the value ofE/N required to sustain an avalanche as the peak sustained current(correspondingly the electron number density) reaches its design level.Thus, the controlled avalanche pulse potential across the dischargefalls well below its impedance-matched potential value in a time muchshorter than its impedance-matched, pulse-forming network's time period,as a result of the load impedance having fallen well below the network'simpedance at the design point of peak plasma conductivity.

The specific requirements of the controlled avalanche pulser are:

(1) To provide a pulse sequence, wherein each pulse rises to an E/Nvalue of ˜180 Td under open circuit conditions (at 50 Torr-Amagatdischarge conditions, the corresponding potential may typically reach180 KW).

(2) Under residual ionization conditions, where the ionization level hasdecayed to its minimum value following the off period of the pulser andat the onset of the next pulse, the E/N value is clamped to a value of˜80 Td to ˜120 Td (according to adjustment of circuit parameters).

(3) Upon completion of the avalanche needed to restore lost ionizationto maintain the correct mean level of ionization, the E/N value must, byinteraction with the current, have fallen to a level insufficient tocontribute to further ionization—typically less than 40 Td.

(4) The rise time of the controlled avalanche pulse is less than 30nanoseconds, but preferably less than 15 nanoseconds, and mostpreferably less than 5 nanoseconds.

(5) The impedance-matched pulse width is to be less than 75 nanoseconds,but preferably less than 30 nanoseconds, and most preferably less than15 nanoseconds, provided that the rise time can be achieved on the orderof 5 nanoseconds.

(6) The “jump start” pulse should be capable of sustaining current flowat the voltage corresponding to a plasma E/N of ˜150 Td to ˜180 Td ormore, and at a current level characteristic of the controlled avalanchepulser impedance operating into a matched impedance load.

(7) The rep rate is to be adjustable and must equal or exceed 20,000pulses per second continuously, and the pulses must be triggerable ondemand.

However, in order to excite the highest density flow stream which mayreach 150 Torr-Amagat for the case of ionizing very high-powered lasers,the method may require pulsing at higher repetition rates than may bederived by a single controlled avalanche pulser. This is because theionization loss rate increases with increasing density. In such cases,the rep rate obtainable from a single pulser may be doubled, tripled, oreven quadrupled to as much as 100,000 pulses per second, simply byinterleaving the pulses from 2, 3, or 4 modules which individuallyoperate at 20,000 to 25,000 pulses per second and function according tothe aforementioned specifications. Each of the units must beappropriately synchronized and time-delayed with regard to each other.Then, the 2, 3, or 4 individual pulse trains are simply added.

Example of Pulser Circuit

The design of a controlled avalanche circuit depends on, for example,the power range of a particular laser. The example presented below issuitable for an approximately 20 KW continuous power laser. In general,the design principles of this example are suitable for lasers of averagepower falling between approximately 5 KW and approximately 150 KW.

FIG. 17 illustrates a controlled avalanche, or “pulser,” circuit inschematic form. For purpose of illustration, circuit connections areshown as lines or wires. In actual circuits, high speed,impedance-matched mechanical structures such as, but not limited to,coaxial cylinders, strip lines, or wave-guides are used. An actualpackaged circuit as represented by the schematic of FIG. 17, therefore,may physically resemble the circuit shown in FIG. 18, a description ofthis figure follows below.

Referring to FIG. 17, the pulser circuit and O₂ ¹Δ plasma generator areillustrated together, since in practice the two units are inseparableand do interact to form a unified circuit. As shown, the pulser circuitsits on top of the DC power supply 1101, which provides the excitationpower at a potential which maintains temporally constant, but perhapsspatially graded plasma conditions at or near a value of E/N ofapproximately 10 Td. A large capacitor 1102 is used to stabilize voltageconditions during a fluctuating current load, and to bypass theavalanche pulses, thus referencing these to ground potential. Typically,the required pump potential will fall between approximately 7 KV andapproximately 20 KV, depending on gas density and generator tube length.

The pulse forming network of the circuit consists of four sets ofstacked cable Blumlein lines 1111, and are wired so that theirpotentials add at the output end. A fifth set of cables 1112 form afinal Blumlein line whose potential is added onto the top of the firstfour lines. The first four stacked lines provide the primary pulse trainwhich maintains ionization while the fifth line powers the heliummeta-stable generators which are located upstream of the O₂ ¹Δ generatorplasma tubes, and serve to provide a volume-distributed source ofinitial pre-ionization.

For the case of a 20 KW class laser, each of the five lines consists oftwo approximately 50 ohm coaxial cables, such that their switchedimpedance on the front end is approximately 5 ohms. If the line has beencharged to approximately 20 KV, then approximately 4 KA will flowthrough the thyratron switch 1103. In turn, the four line segment willhave an output impedance of approximately 400 ohms, thus generating anapproximately 200 amp pulse at approximately −80 KV if the load werematched to the line at 400 ohms. Note, however, that in the absence ofionization, the output voltage doubles to approximately −160 KV at zerocurrent. The fifth line provides approximately 200 amps at approximately−20 KV lying on top of the approximately −80 KV primary output inaddition to the DC pump potential (perhaps −10 KV) in the case whereboth circuits are loaded into their matched impedances: approximately400 ohms and approximately 100 ohms, respectively.

When impedance-matched, the pulse output is a square wave whose pulsewidth matches the two-way propagation time through a single cable. Forexample, approximately 30 nanosecond wide pulses will be produced whenthe cable lengths (individually) are cut to be approximately 10.6 feetlong, where the cable's index of refraction is assumed to beapproximately 1.4—the value which is characteristic of a 50 ohm cable.

In order for the Blumlein lines to function as intended, they must bedischarged by the thyratron during a time period which is short comparedto the line's two-way pulse propagation length. This is accomplished byusing an ultra-fast (pre-ionized), low-inductance thyratron 1103 incombination with a METGLAS® saturable magnetic switch core 1113, and byusing an impedance-matched current distribution structure. This switchis for simultaneously grounding the front ends of the Blumlein lines tolaunch pulses, each time the front ends are grounded one pulse islaunched. The METGLAS® core may be reset between pulse firings by meansof a floating DC bias current winding on the core.

The basic sequence is to pulse-charge all of the cables from a highvoltage power supply 1106 through a triggered command charge circuitconsisting of a vacuum tube 1107 and an inductor 1108 which transfersthe charge in a time period defined by approximately the resonant halfperiod of the reactor's inductance and the cable's net totalcapacitance. The tube 1107 also prevents the cable's charge from flowingbackward, since the resonant transferred voltage is nearly double thatof the charging supply. Note that when the positively charged cableBlumlein lines are switched to ground at the input, a negative highvoltage pulse is produced at the output.

Both thyratron and vacuum tubes are controllable by electronic circuits,which are schematically represented by boxes 1104 and 1109,respectively, and which are powerable by floating isolation transformers1105 and 1110, respectively.

The following describes how the outputs of the cable Blumlein lines aredistributed to the array of plasma tubes and their meta-stable heliuminjection pre-ionizing sections, and also the means by which excessenergy is discarded to allow rapid fall time. In general output ends ofthe Blumlein lines are connected serially. Before continuing thisdescription, however, elaboration of a few details is helpful. The lastcable comprising the fifth Blumlein line section is shunted across itsoutput through inductor 1115 in order to remove residual charge prior topulse charging it (otherwise the line would float). Next, a short length1116 extension has been added to the output of the ionization pulse linein order to delay the main generator tube's excitation with respect tothe pre-ionization.

Finally, the entire string of pulse cables are shunted with a secondsaturable reactor magnetic switch into a large capacitor, which in turndischarges into a resistor 1114, this is also referred to as a snubbercircuit. The magnetic switch holds off conduction for a specified timeperiod, then dumps residual energy (which may be bouncing around due toimperfect impedance matches). This allows the applied potentials to fallin direct response to the plasma, thus circumventing an elevatedpotential to exist beyond its desired point in time. Again, thesaturable magnetic switch must be reset between pulses by means applyinga DC bias current to the METGLAS® core.

A number of pulsed ground potential connections must be distributedthroughout the generator plasma array to enable low inductance currentreturn. These are each passed through blocking capacitors 1124 in orderto ground the pulses while blocking the DC potential, above which thepulse network must float.

A single pulse module comprising ten cables, and one thyratron switchcan power as many as, for example, but not limited to, 80 plasma tubegenerators with their meta-stable pre-ionizer sections. In thisparticular example, each tube-pre-ionizer assembly consists of a BeO orAl₂O₃ tube 1122, an anode/input nozzle 1121, an oxygen and heliumreservoir 1117 into which all of the oxygen and most of the helium isintroduced, a metal tube 1118 into which some helium (and/or optionallyargon is introduced), an anode 1123, and an auxiliary electrode (orelectrodes) 1125, which is used to jump-start the ionization process andpossible to help grade the DC pump potential.

The pre-ionization potential is applied between the metal heliuminjection tube 1118 and the cathode 1121 to provide the pre-ionizationpulses. Note that the main discharge cathode serves as an anode for thepre-ionization pulse (the inside of the helium injector tube forms a hotcathode space charge layer which serves to generate meta-stable helium).

The two pulse output busses, residing for example at about −160 KV opencircuit and −180 KV open circuit, respectively, are distributed to thetubes through isolating/ballasting inductors 1119 and 1120, one for eachof the two circuits and for each tube.

Finally, the intermediate electrodes 1125 are connected throughballasting inductors 1126 (one for each tube) to the jump-start pulser.This pulser provides upon start-up, only one low impedance pulse at apositive polarity which is opposite from the upstream negative polarity.The two potentials are additive (for example, −180 KV+50 K) over afraction of the tube's total length, thus facilitating rapid initialbreakdown.

Referring again to FIG. 18, referenced above, a controlled avalanchecircuit mechanical assembly 1200 is shown. A transmission line 1202 isshown centrally surrounded by cable Blumlein lines 1204, 1204′. Athyatron 1206 is shown centrally connected to the transmission line 1202and in connection with floating thyatron control electronics 1208. Acurrent return 1210 is also shown.

Referring to FIG. 19, an alternative means 1300 of floating a DCpotential on top of a DC jump potential and the pulsed high voltageavalanche ionization potential is shown. Compare to the fifth set ofcables that form a final Blumlein line whose potential is added onto thetop of the first four lines 1012, as shown in FIG. 17. The alternativemeans 1300 comprises a high voltage blocking inductor 1302, for example,preferably wound from coaxial cable, that is connected through aresistive device 1303 to the helium supply inlet 1304 that feeds agenerator tube 1306. An oxygen and/or inert gas supply inlet is alsoshown 1308. Also shown in FIG. 19 is a high voltage pulser 1310, a DCsupply 1312, and a source of DC pre-ionization voltage 1314. Electrodes1316, 1316′ of the generator tube 1306 are shown bounding at the ends,of course, the electrodes may number more than two per tube and belocated at a variety of points along the tube.

Longitudinal Beam in Supersonic Throat Arrangement

The present invention also includes a laser comprising a gas, a beamproduced by the gas and a throat wherein the gas and beam pass throughthe throat. In one embodiment, the throat comprises a converging regionand a diverging region to achieve supersonic flow of gas passingtherethrough. A laser according to this gas flow/beam arrangementembodiment 1400 is shown in FIG. 20 (e.g., an axial cross-sectionthrough a substantially cylindrical structure). Lasers according to thisembodiment are optionally suitable for power outputs of approximately 5to approximately 20 kW. According to this embodiment, a beam 1402 passesthrough a gas flow throat 1404. As described in other embodimentsherein, this laser 1400 is capable of either closed or open cycleoperation and comprises some features of, for example, the laserapparatus shown in FIGS. 15 a and 15 c. For instance, as shown in FIG.20, this embodiment comprises at least two oxygen supply ports 1424,1424′, at least two helium supply ports 1428, 1428′, at least two iodinesupply ports 1432, 1432′, an O₂ ¹Δ electric generator/heat sink assembly1450, and a resonator cavity 1460. Of course, embodiments comprising asingle supply port for oxygen, a single supply port for helium, and/or asingle supply port for iodine are within the scope of the presentinvention, as are headers and/or other distributors for the same.According to one embodiment, oxygen and iodine are supplied at a ratioof approximately 50 to 1. Adjustments to the oxygen to iodine ratio areuseful for controlling gain.

The O₂ ¹Δ electric generator/heat sink assembly 1450 of this particularembodiment comprises at least two tubes 1452, 1452′. Each tube issurrounded by a heat sink or heat exchanger, which optionally providesfor flow of a coolant or heat exchange fluid (including gas), asindicated by coolant inlets 1456, 1456′ and outlets 1458, 1458′. Ofcourse, the inlets may optionally serve as outlets and vice versa. Whilethe tubes shown in FIG. 20 are substantially parallel to the beam,embodiments comprising tubes that are arranged at other angles withrespect to the beam are also within the scope of the present invention.An embodiment comprising at least one annular region that provides forcarrying oxygen and/or helium gas is also within the scope of thepresent invention and a heat sink and/or a heat exchanger for use insuch an embodiment optionally comprises an annular cross-section.Further while iodine inlets 1432, 1432′ are shown in FIG. 20 positionedperpendicular to the beam axis, an inlet or a plurality of inlets areoptionally positioned parallel to the beam axis or at any angle to thebeam axis. While not limiting, it is preferred that iodine enters andmixes the gas prior to the throat 1404.

Based on the discussion of other embodiments presented herein (e.g., seediscussion of FIG. 15), one of ordinary skill in the art wouldunderstand that the embodiment shown in FIG. 20 also comprises a powersupply and electrodes. Of course for low pressure operation and othertypes of operation, the invention does not have to rely on thisparticular apparatus or method of forming metastable helium. Othermethods and apparatus for providing seed volume ionization are withinthe scope of the present invention and known to those of ordinary skillin the art.

The laser beam of the embodiment shown in FIG. 20 is produced in theresonator cavity 1460. Gases in subsonic flow, mixed with iodine, enterthe inlet side of the throat 1404. This mixture of gases expands in thesupersonic expansion region of the resonator cavity to achievesupersonic flow. In a particular embodiment of the invention, gasleaving the throat comprises a velocity of approximately Mach 2.5 toapproximately Mach 3. The gas further optionally comprises a temperatureof approximately 112 K or lower and/or experiences a pressure drop ofapproximately one order of magnitude.

While the arrangement shown in FIG. 20 comprises a single beam 1402 thatpasses through a single gas flow throat 1404 alternative arrangementscomprising a plurality of throats and/or a plurality of beams are withinthe scope of the present invention. In general, the beam diameter 1402is substantially matched to the diameter of the throat 1404. In theembodiment shown in FIG. 20, the beam 1402 is bound by two mirrors 1412,1416. One of the mirrors, for example, but not limited to, the leftmirror 1416, comprises a partially reflective surface that allows forpartial transmission of the beam 1402. Of course, the other mirror 1412optionally comprises properties that allow for transmission to form, forexample, a dual beam apparatus. Alternatively, the left mirror 1416 doesnot allow for transmission and the right mirror beam is partiallyreflective. This embodiment further optionally comprises an unstableresonator, for example, but not limited to, a system wherein at leastone mirror comprises an annulus for output of an annular beam.

Referring to FIG. 21, a diagram of a beam 1402 is shown. Note that thebeam diameter increases from the throat 1404 to the right mirror 1412.Also note that the right mirror 1412 comprises a concave surface. Thesurface is concave to account for changes in the phase front (see dottedline near right mirror 1412)—in most instances, the phase front at thethroat is substantially flat (see dotted line near throat 1404). Ofcourse, compound elements are optionally used at either end to correctfor phase front distortions and/or to focus the beam.

According to one embodiment, the length is sufficient to extractapproximately 5% of the energy from the excited gas. The embodimentshown in FIGS. 20 and 21 is generally applicable to any transfer typelaser. More specifically, such an beam/cavity arrangement is useful whenkinetics allow for the lasing molecule to be recycled many times overthe length of the cavity. For example, a transfer molecule (e.g., butnot limited to, iodine) may be energized and lased from approximately 10times to approximately 100 times over the length of the cavity. Thisallows for gain and, again, is controllable by, for example, adjustingthe ratio of lasing molecule to non-lasing molecule(s) in the gas. Inone embodiment, the cavity comprises a length from approximately 0.1 toapproximately 2 meters.

The throat 1404 of the embodiment shown in FIG. 20 has, for example,characteristics that allow for a particular mass flow rate. Such athroat optionally comprises an upstream converging region and adownstream diverging region. Characteristics of converging, throatand/or diverging regions are useful for providing a particular Machnumber, for example, but not limited to, Mach number of approximately 2to approximately 3. As shown in FIG. 20, the resonator cavity expansionregion (from throat 1404 to right mirror 1412) comprises an increasingcross-section. The increasing cross-section helps to account forboundary layer growth, which, in turn, helps to reduce shocking down ofthe gas in the cavity. While shocking down of the gas in the cavity maybe tolerated, in most instances, shockdown occurs in a region removedfrom the beam path. For example, referring to FIG. 20, shockdown occursin, or proximate to, a substantially annular region 1420 adjacent to adiffuser structure 1408 that comprises part of a subsonic diffuser. Asshown in FIG. 20, the diffuser structure 1408 also optionally comprisesthe right mirror 1412 or provides an attachment point for such a mirror.

While the above description makes reference to particular values, suchas, but not limited to, an E/N value of approximately 180 Td, it isunderstood to one of ordinary skill in the art that lower E/N values arewithin the scope of the present invention, for example, approximately150 Td and below. The above description also makes reference to “plasma”which is used generally to describe a weakly ionized gas, for example,but not limited to, a gas with an electron density between approximately10 to approximately 10¹⁵ electrons/cm³.

Various embodiments of the present invention are useful for thefollowing areas:

1. Energy and Nuclear Power—cut-up decomissioned reactor vessels,centrifuges, etc.; scabble radioactive layers from cement surfaces; anddeep penetration welding, which may be performed robotically incontaminated areas.

2. Marine and Heavy Equipment Industries—deep penetration welding,cutting and drilling; cladding, surface modification or texturing;removal of corrosion and sea debris, such as barnacles, from marineplatforms and barges; and removal of coatings and special, rubber-likelayers from vessels, such as, but not limited to, submarines, ships, andbarges.

3. Civil Engineering—cleaning bridges, tunnels, outdoor storage tanks(inside and out); road texturing; and tunneling, mining, and rockfracturing.

4. Steel Industry—remove scale from steel rolls and steel rollbutt-joint welding.

5. NASA/Space Industry—destruction/removal of space debris; meteordeflection from Earth and other objects; rocket propulsion fromground-based laser or from solar-powered, space-based laser (at anyaltitude above Earth's surface); deep space communications; and spacepower transmission.

6. Military Applications—Target designators and ground-based (fixed ormobile), airborne, or space-based weapons.

7. Automobile Applications—reducing emissions from automobile exhaust(as well as any other combustion engine).

The preceding examples can be repeated with similar success bysubstituting the generically or specifically described reactants and/oroperating conditions of this invention for those used in the precedingexamples.

Although the invention has been described in detail with particularreference to these preferred embodiments, other embodiments can achievethe same results. Variations and modifications of the present inventionwill be obvious to those skilled in the art and it is intended to coverin the appended claims all such modifications and equivalents. Theentire disclosures of all references, applications, patents, andpublications cited above are hereby incorporated by reference.

1. A matched impedance controlled avalanche driver circuit for excitinga plasma, said circuit comprising: a preionization device forpreionizing a gas; a pulse forming network charged to a first voltage; atransmission line connecting the pulse forming network to at least twoelectrodes, said transmission line and electrodes for transferringelectrical energy to the preionized gas; wherein a capacitance of saidtransmission line is chosen to increase said first voltage to a secondvoltage sufficiently high enough to ionize the gas to a plasma; andwherein an impedance of the plasma matches an impedance of said pulseforming network, thereby enabling said pulse forming network to pump alaser transition in the plasma at a potential below a glow potential ofthe plasma.
 2. The circuit of claim 1 wherein said pulse forming networkcomprises distributed lines.
 3. The circuit of claim 1 wherein saidpulse forming network comprises discrete elements.
 4. The circuit ofclaim 1 wherein at least one of said electrodes is shaped to preventfield enhancement.
 5. The circuit of claim 1 wherein said transmissionline comprises at least one transfer capacitor.
 6. The circuit of claim1 further comprising a switch comprising a spark gap or a thyratronswitch.
 7. The circuit of claim 6 wherein said switch is low inductance.8. The circuit of claim 1 wherein said transmission line comprisesparallel cables.
 9. The circuit of claim 8 wherein said cables areimpedance matched to said pulse forming network and the plasma.
 10. Thecircuit of claim 1 further comprising a snubber circuit electricallyconnected between said electrodes.
 11. The circuit of claim 10 whereinsaid snubber circuit is used to adjust the second voltage, therebyensuring that the impedance of the plasma substantial exactly matchesthe impedance of said pulse forming network.
 12. The circuit of claim 1generating at least one pulse comprising an ultra-high narrow voltagetransient followed by a lower-voltage flat wave form.
 13. The circuit ofclaim 12 wherein said transient and said flat wave form areindependently controllable.
 14. The circuit of claim 1 incorporated intoa repetitively pulsed gas laser.
 15. The circuit of claim 14 wherein arepetition rate of said gas laser is up to approximately 200 pulses persecond.
 16. The circuit of claim 1 wherein said preionization devicecomprises a pulsed X-ray source.
 17. The circuit of claim 16 furthercomprising a high voltage pulser to drive said X-ray source.
 18. Thecircuit of claim 16 wherein at least one of said electrodes comprises anX-ray window.
 19. The circuit of claim 18 wherein said window comprisesberyllium.
 20. A controlled avalanche pulser circuit for exciting aplasma, said circuit comprising: one or more Blumlein lines forproviding a primary pulse train; a pre-ionizer connected to at least oneinjection tube and at least one first electrode; an ultra-fast thyratronswitch connected between input ends of said Blumlein lines and a powersupply; at least one second electrode connected to said Blumlein lines;and a plurality of ground potential connections connected to said atleast one first electrode for providing low inductance current return.21. The circuit of claim 20 wherein each of said ground potentialconnections comprise a blocking capacitor.
 22. The circuit of claim 20wherein said pre-ionizer comprises a Blumlein line.
 23. The circuit ofclaim 20 wherein said pre-ionizer comprises a high voltage pulser and atleast one high voltage blocking inductor connected to said high voltagepulser and said at least one injection tube.
 24. The circuit of claim 20further comprising a snubber circuit connected to said pre-ionizer. 25.The circuit of claim 20 further comprising one or more auxiliaryelectrodes.
 26. The circuit of claim 20 wherein said Blumlein linescomprise stacked cable Blumlein lines.
 27. The circuit of claim 26wherein output ends of said Blumlein lines are connected serially. 28.The circuit of claim 26 wherein each of said Blumlein lines comprises atleast two approximately 50 ohm coaxial cables.